Ok, well here it goes. I am going to assume that most people do not actually know much about the system so I will provide some mechanical explanations as I go along.
Campaign Building
Building a GURPS campaign is probably the most difficult part of GMing in the system. GURPS is less of a game system and more of a game engine. Unless you are playing one of the pre-built settings of which there are a few, the GM has a ton of work ahead of them. Essentially you will have to decide which rules you are using. I do not mean just selecting which books you are going to use, but what rules within them you are going to be playing with. This is not just going with the two core books and calling it a day. I do not even play with a lot of those rules in those two books.
Really, every rule except how to build characters, probably a few damage rules, and dice resolution is pretty much optional. I will go into more details later, but you can (and I have and it works really well) play GURPS as an extremely rules light system where you just do not use most of the rules. The average GM probably will probably not run such a rules light, but if many rules just seems like excessive bookkeeping (because things like bleeding rules are) it is best to just not use them. If you GM the system a lot it becomes kind of clear as to what rules you’d want to use or not.
Beyond choosing what rules to not to use, you’ll also have to make some selections between different rule sets or tweaking them. For example, there is not a single magic system. Off the top of my head, I was able to come up with ten different magic systems (and I think I am missing some). Obviously, you are not going to play with all ten of them at the same time, so you will have to decide which system(s) you would be using. A small personal experience note here, having experimented with many of the systems, the basic magic system is probably the best for your average player. The flexible magic systems where players can build their own spells are really cool, but it takes a certain type of player to actually use them as I counterintuitively find most of my players just kind of shut down when their magic can do anything. So instead, they do not use their magic and do nothing. Plus building custom spells at the table can take a while and slow the game down.
Another small note here is book selection. This is something not very clear, but when you go beyond the basic rules book the additional books replace the rules in the basic book sometimes rather than adding onto it. This is mainly for equipment. So as an example, there is a bunch of equipment that you would use in your average basic fantasy game found in the Core books. Things like swords, armor, etc. If you decide to use the Low Tech book, all of the players should only purchase equipment found in the Low Tech book and ignore any of the equipment in the basic book except for the few items that are not relisted in Low Tech (there are a few). Essentially, the items in the Core book were considered good enough to ship the books, but each of the Tech books provides a much more in depth and expanded selection of items and also just ends up updating cost and stats of all of the existing items from the base book.
After rule selection there is still a lot of work to be done during campaign prep. For example: each race is a collection of stats and so unless you are just using something prebuilt the GM has to author every single racial template for the campaign. The other thing that is pretty big to do is coming up with clear guidelines as to which individual advantages, disadvantages, and skills can be purchased by the players.
Also, the starting character point totals, which will really depend on the type and feeling and genre of the game you want to play. For fantasy, I have done both 100 and 150 character point games and the difference is quite noticeable. 150 character points feels pretty heroic compared to the much weaker and grittier 100 point characters (and 100 point characters really powers down mages significantly with the basic magic system as the way you build a mage is you have a massive upfront point cost and then each new spell you learn costs 1 character point so you scale with the number of spells you know much better than say a melee character). I know 250 character point characters are pretty popular as well, but I can not even imagine how powerful those characters would feel. When you go out of fantasy though, you will need completely different starting point totals. I would probably go up to 250 character points (or even higher) for say a super powers game, but I have also gone down to 25 point characters if I just want the players to be average humans in say a horror game. Usually the way I figure it out is buy building a few characters of the power level I feel would be appropriate for the game and then using that as a guideline for starting character point totals.
One last thing in this section, if the players will never see it, do not bother with character point totals or making it perfect. You do not need to create perfect enemy and monster stats and know what their character points are. I just slap down how much ST, DX, INT, HT, DR and a few skills and abilities and be done with it. If the character point totals matter (such as a player taking an ally) then you need to create a full stat template, but 99% of the time doing that is a waste of time.
Character Creation
Character Creation in GURPS is probably one of the longest processes in the game. I personally think it is super fun, but it is not for everyone. This is also where the infamy of GURPS crunch is. Character creation is very crunchy and I would highly recommend using a tool to actually build characters (there is a paid one, but I use and prefer
https://gurpscharactersheet.com/).
Unless I already know the player, and they know the system, I generally sit down with each player for a few hours and build their character with them. Especially for new players it is overwhelming. Unlike most games, which have simplified the number of skills you have access to, GURPS has the opposite approach where there are skills for everything. For example, the ten five skills are Accounting, Acrobatics, Acting, Administration, Aerobatics, Airshipman, Alchemy, Animal Handling, Anthropology, and Aquabatics. As you can see everything is very specific and also due to the nature of the system, has to cover everything. This makes it hard for new players to find the actual relevant adventuring skills for the campaign. On the other hand, this does make it really fun for people who like to really tweak their character and spend points in flavor skills to really flesh out the character they are playing.
Another thing to watch out for new players is that they tend to build very worthless characters and spread out their points into lots and lots of skills, but only have them at a level of 12. This tends to make the character actually useless as they can not reliably do anything and especially if any of those skill rolls are usually opposed rather than a straight check then they are really screwed. I once played a game where our rogue character only had a skill of 12 in stealth. It did not go well for him, and he was captured, and the GM had his hand cut off for being a thief. It was quite humorous for everyone else involved.
Another thing to watch out for is Disadvantages. Disadvantages taken at character creation give the player extra points to spend. This means that savvy players can get more power by taking more Disadvantages. I have never actually seen a player do this to such a degree it would be a problem. Instead, I have seen players just take so many Disadvantages they become worthless as they constantly have their Disadvantages screwing with them. There is a rule for a Disadvantage limit that kind of solves both of these problems where players can only take so many points in Disadvantages. I generally set the limit at -50 which feels good to me.
On the other hand, players who do know the system and especially if there are supernatural powers of any sort allowed can completely abuse it and make really overpowered things. The system has a whole mechanism for building your own powers and can easily be munchkined. So the GM needs to keep a watchful eye on those types of players too.
Just remember, do not be afraid to say no to a character. It is your only defense.
I would say your ideal GURPS player is someone who likes to role play, likes number crunch, and would rather play an interesting character rather than an overpowered one. Because there are no classes within the system the player can be a bit more freeform with the characters they build (as long as the GM allows it). Like if the player wants to make a character who is a gryphon rider. That is something that is doable on even a 100 character point budget where it is something not really viable to make in a system like D&D.
Actually Playing
Playing a GURPS game is actually the easiest part of it. Almost all of the complexity of the game is front loaded into character creation. All that crunch and math is pretty much gone when you actually get into the swing of thing and there’s merely some simple addition. The key to GMing a GURPS game is to make heavy use of the task difficulty table. Whenever the player uses a skill the GM should assign a difficulty bonus/penalty to the roll. Anything mundane and not in “adventuring conditions” should probably be assigned a +4-6 or just not even have a roll (remember, only roll when failure would be interesting). Many rolls do have specific modifiers for conditions, but since every rule is pretty much optional, the GM can instead just say, all my discretion with the table. This can even be taken so far as to removing tactical combat from the game entirely and instead just handing out skill bonuses to what type of attack the player says they are doing in combat. This is why GURPS at its core is actually a very much roll and shout game despite looking like a super crunchy system from the outside.
Now my guess is that most GMs would not be removing tactical combat. That is the one thing that probably will slow the game down significantly. Especially for new players and GMs. Each GURPS round is really short: 1 second. This means that the number and types of actions that the players get is not what most players are used to. Usually you do one thing: move or attack, not both. There is a Move and Attack action, but it is not good as you get very harsh penalties because it is actually simulating you attacking while running (It actually has a use for really high speed characters who are taking a swipe as they run by someone, but that is not something most players would run into). Ranged characters end up taking their actions over multiple turns a lot of the time. For example an archer has to spend a turn pulling an arrow out of the quiver, drawing the arrow back, optionally a turn(s) aiming, and then another turn firing the thing. This means melee have made multiple attacks in the time it takes an archer to fire a single shot. This is not even touching if you have a game with early firearms where some of the weapons take 60 turns to reload.
Melee combat itself also can really easily turn into a whiffing battle. GURPS has relatively low health pools and so getting hit once or twice can easily bring characters down (especially unarmored ones). As a side note here, while the characters do tend to go down pretty quickly and are taken out of a fight, they actually are decently resilient to actually dying. Still, the best way to survive in the game is to not get hit. Combat resolution is far less abstract than say D&D. Characters have the ability to parry with a weapon, block with a shield, dodge the attack completely, or have it hit their armor all as separate things. Each time there is an attack then the defender gets an active defense roll (unless the attack was from behind so they did not know it was coming). This means there are a lot more rolls per attack in the game instead of just comparing against AC. This also means that even though the players might be making their attack rolls the enemies might have high enough active defense rolls that the players can never get through. It is important to get players into the mindset to actually use their Feint and Deceptive Attack rules to get through the active defenses of their opponents. When done correctly, GURPS melee combat kind of becomes a dance of trading blows which feels pretty cool, but I think the learning curve to get to that point is a bit steep and requires both the players and GM to be on top of all of the options of melee combat.
I know this got a bit long. I guess that is kind of my basic advice for the system. I personally love it because as a GM who makes all of their own settings the power the system gives me is insane. I can easily run games such as world hopping portal fantasy where the players have a bunch of modern firearms and are going up against dragons and knights. Or do crazy Sci-Fi Fantasy settings with spaceships and futuristic tech residing next to magic. As someone who loves world building and putting together crazy settings the system just gives me so much power to put together whatever I want, unconstrained by whatever I am building it in while still providing a grounded and less narrative based system. Plus, I like number crunch so that helps.
