A few, simple things that will give you the best ROI on your car:
1. If you buy a car used, replace the oil and consider replacing brake, transmission and radiator fluid. I like to start from a known maintenance interval. Many poorly maintained cars never have had brake, trans, or radiator fluid changed. For a 4wd, change the front and rear axle fluid, consider replacing transfer case fluid if over 60k miles.
2. Most modern cars have oil sensors that measure certain features of the oil (resistance, viscosity, water content), or that have algorithms that figure out how long the oil should last based on oil temperature and driving conditions. The car will tell you when it needs an oil change. When it does, do it within 500-1000 miles. I use 100% synthetic in my rides and it lasts 9-12k miles between changes, but at least once a year. 3k oil changes are completely unnecessary unless you're driving a taxi or in the desert. Check oil level every gas fillup. Some cars now have oil level sensors in addition to quality sensors, which are handy.
3. Check tire pressure, even if you have a TPMS system, every other fuel fillup, or monthly, whichever is less. Also check when seasonal temperature changes happen in summer/winter.
4. Rotate tires every 6k miles. This is easy to do yourself. Consider winter/summer tire sets, or five tire rotation methods. I use winter/summer. I admit I'm sometimes lazy about this and shorten my tire life by rotating less often.
5. Change air filter every 12k miles. This and tire pressure make up most inefficiencies in car maintenance.
6. For 4wd vehicles, replace front and rear axle fluid every 24-36k depending on use.