I do 5e but I'll try to give some general tips.
-Learn magic and Matrix rules like you're an autist. It's the hardest part of the game so learning it will make your life easier.
-Use the Rule of 12 when statting combat. Random Security Guard #5 doesn't need a whole stat block. Just make him good at what he's good at.
-Vehicle stats on the other hand are extremely important.
-Learn to improvise. The runners will ALWAYS attack the problem in the ONE way you didn't plan for.
-Print maps and mark the locations of cameras and stuff on them. It'll maker your life easier even if it's a theater of the mind set up.
-NPCs should be somewhat memorable if the runners are meant to interact with them a lot. Pick one or two quirks.
-Make sure your runners actually use their contacts, and have their contacts use them. Great plot hooks.
-Most importantly, this is not D&D. Fighting is best used as a last resort or in the Sprawl somewhere. Plan the game like a puzzle the characters have to solve, and don't put in stuff they can't handle (i.e. If there's no mage don't drop in a bunch of magical security or if there's no hacker don't assign datasteals).
I fully intend to wing it when it comes to lore, but mechanical knowledge is harder to fake.
Okay, hopefully all your players are new because Shadowrun lore autists are obnoxious as hell. Trust me on it.
EDIT: Oh, and I almost forgot. Going along with the "It's not D&D" point, runners may have very good reasons for refusing a job. Have a couple missions ready to go, or go full expert mode and just start pasting new names on the only job you did make. For example, earlier in the thread I mentioned my group was given a job to steal a flatvid that may or may not have a blood magic ritual on it. The client's some weeb but it would also make sense if the client was from Aztechnology, the Atlantean Foundation, or even the Draco Foundation.