Stay on top of changing your fluids. Oil changes are a lot cheaper than a new engine (plus labor) or any other big component of your car, like transmission or radiator. Change your engine oil (about every 5K miles), transmission fluid, engine coolant, brake fluid (every 3-6 years), diff fluid (if you have a differential), transfer case fluid (if you have a transfer case), and power steering fluid (if it’s hydraulic based)

If you live in a salty area (i.e. a place that snows a lot), learn how to apply Fluid Film or any oil-based thin film for rust prevention under your car. It’ll keep the car going for a lot longer and fluid film is a lot cheaper than a new sub frame or structural component of your car

Service manuals from the manufacturers are available for subscription, but if you know where to find them, I’d be curious to see, because my search engine skills have gotten worse as time has progressed. I think Toyota and Honda sells their subscription for 2 days of access for $20 and you should be able to download the relevant PDFs you want

As for appearances for you car, don’t eat or really keep anything in your car, unless it is for the car and its emergency kit. So I try to take everything out of the car with me if my car doesn’t need it like clothes, groceries, or anything like that. This makes car break-ins less likely to occur, and if it does, it’s more of a bad day or two (depending on your skillset/money you have) instead of a gut-wrenching moment when you realize they stole a sentimental valuable. Don’t park under trees to avoid leaves or tree sap. Neither under power lines because of bird poo

Remember that cars are depreciating tools to get you from point A to point B. The most important part of it is that it’s mechanically sound and the safety features for it work. The next part is that it blows cold AC and hot air for heat. Anything beyond that is a bonus