Learn to fix things yourself. Mend your clothes, fix your bike or car, patch drywall, whatever. Learning to do things gives you the option of to save money doing it yourself. If you don't learn, your only option is to pay someone else to do it.
Changing the oil in your car only requires a spanner, pan, and household stuff like cloth rags. You can do it in your driveway faster than you can drive it round-trip to the dealership. I've saved heaps over the years.
House painting is a good skill. I knocked over $20k off my house build price by picking up a paintbrush. It was about 2 weeks of work and maybe $1k in supplies.
Learn computer maintenance. Like, how to format it and start over. How to diagnose and fix small issues. So many people buy new computers just because their old one is clogged with cruft. I fixed computers that others threw out, and avoided upgrade costs for decades.
Most importantly - learn to cook. Home cooking is so much cheaper.
Changing the oil in your car only requires a spanner, pan, and household stuff like cloth rags. You can do it in your driveway faster than you can drive it round-trip to the dealership. I’ve saved heaps over the years.
Are your car services limited to changing the oil? Because mine aren't. They include all kinds of checks for degrading parts (filters, brake pads etc), and while I could possibly do all that myself if I had the time and could get hold of a shop manual for my car, I'd also need to acquire the parts first. On the other hand, my car doesn't need changing oil outside of the 15000km service interval.
What you absolutely should learn is how to change a tyre. So many people don't know how to do it and have to get assistance when they have a flat...
When I was new to it, I would just do the oil, then get the shop to do the other stuff. Fluids and filters are the low-hanging fruit. They charge a huge amount for something that requires little skill or equipment.
Once the dealer quoted me $300 to change the radiator fluid. I didn't even own a garden hose at that point, but I bought one, figured out how to flush coolant, and saved about $250.
Later on I started doing brake pads, gearbox oil, suspension bushes and little tidbits. The only "service" I paid for in the last 3 years is a head gasket replacement. Hopefully I get another 20 years out of it.
Same goes for home repair. Learn to spackle and patch drywall, change a doorknob, install a toilet, snake a drain, and replace a capacitor or heating element in your hvac system. These are things anyone can learn to do with minimal tools and inexpensive parts, but will cost hundreds to hire a professional.