Replacing the fluids in the car and maintaining them at the proper levels is very important in ensuring that the car runs well and for many miles. That does not just include the motor oil and anti-freeze, but also the transmission fluid, brake fluid, power steering fluid, and differential fluid. Replacing them is more than just topping off the fluids in the car when they get low. Over time the fluids degrade, get dirty and lose their effectiveness. If you do not replace them when needed, your car will end up needing a new engine, transmission, radiator, power steering pump, master cylinder, camshaft, etc. All of those repairs are very expensive and cost much more than just replacing the fluid.
The owner's manual for your car will give you recommendations for when to change the various fluids and the specific type of fluid you should use. If you do not have an owner's manual, most car makers now post them online at their website.
One maintenance tip that does not cost anything is to simply pop the hood regularly and examine the condition of the belts, hoses and fluids. Replace any belts or hoses that show signs of wear and tear. Replacing them is much cheaper than repairing the damage they will do to your vehicle if they break. If any of the fluids are low, you need to investigate the cause of the leak. Replace any fluids that are dirty.
When you take your automobile into the shop for an oil change, you should have the mechanic rotate the tires, check their air pressure and check the brakes, c v joints, etc. Taking care of these things when they first begin will keep you from spending a lot of money in repairs if you neglect them. Many larger repair shops will inflate and rotate your tires for free with the oil change. That will keep your tires from wearing out prematurely.
Simply keeping your car and its undercarriage clean will keep it from rusting. Rust does not just eat away at the body of the vehicle, it also eats away at the muffler, axles, tie rods, etc. causing them to fail.
There are two maintenance tips that will not harm your car significantly if you do not do them, but will save you a lot of money if you do. They are replacing your air filter often and replacing your spark plugs periodically. A dirty air filter and clogged spark plugs will drastically reduce your gas mileage and cost you much money at the pump.
The bottom line is that if you take care of your car, it will take care of you. If you have not taken care of your used car, truck, suv or van it probably has developed an expensive problem. In that case, your best option is to donate your car to charity. When you donate car to charity it will help you by making you eligible for a valuable tax deduction of $500 or what the old car sells for, whichever is greater.