I'd say changing your brake pads is the biggest one, plus knowing when you actually need to change them.
Changing your own oil never really made sense to me. It's used as a loss leader by auto shops so they can upsell you on other things. It costs me about $20 less to get full synthetic than doing it myself. Might depend on your area I guess.
- Where I am, it's about the same price to change my own oil as it is to take it to Walmart. However, I like crawling under my cars and pulling on everything to see if something is loose. A oil change guy is never going to give the kind of inspection that you can give to your own wheels. I try to combine oil changes with other jobs like wheel bearings, bushings, under coating, etc.
- I think the biggest way I've saved money is getting involved in my community. My neighbor has a dump truck and another has a front end loader. This was great when I needed to do some land moving on my property. Neither neighbor wanted money, but I paid them both a few hundred and made them some pastries because they saved me thousands. Knowing people in your community is massive. No financial guru told me this was such a big deal.
- I've been learning carpentry. I'm not good at it but that's also been saving me a lot while I upgrade this house to sell it or rent it.
- I pay for a debrid service instead of streaming or cable. I don't feel guilty stealing movies I don't own.
- I pick up as many side gigs as I can and pop that cash right into retirement
- I walk to places when I can. Mostly for the exercise and to clear my head but saving a buck on gas is nice too
- pack you lunch, obviously. Keep lots of snacks in your office or your car or bag. It's a good way to make friends too.
- thrift your clothes. If you must buy new clothes for interviews, weddings, funerals, undergarments, etc., I like Burlington coat factory.
- if you're in the north shut off your natural gas in the spring/summer/fall. That's about $60 a month in my area just for the privilege to turn on my furnace when I don't even need it.
- buying something non-namebrand? Check out eBay! Great prices for one-job tools
- I've found better prices and advice buying stuff at mom-and-pop stores than chain stores most of the time. There's some really terrible ones, sure, but I've struck gold a few times and I'll go back to them every time I need something.
- you can avoid a gym pass if you hike, run, bike ,do community sports, calisthenics, work blue collar, etc. Being in good shape saves you so much at the doctor, and boosts your confidence.
- replace soda and energy drinks with water and coffee
- I wish the combo instapot/air fryer/slowcookers existed when I was dirt poor and living in big cities. I swear they're one of the best ways to cook on a shoestring.
- buy used smartphones online. I break mine about every 3 years. Why spend more than $200 on a phone when I can get last year's flagship with a tiny scratch on the glass?
- have a lot of work parties and events? Ask to help clean up. I get sent home with all of the cheese and meat and fruit you could ask for.
- have something break? Pop in the model number into Google. There might be a video or a forum post with someone with the same issue
- keep good oral hygiene. Getting surgery on your mouth is expensive.
- spend money, and mostly time, on the people who are important in your life