If you take care of your car's mechanical needs yourself, you should check up on several systems regularly.
Engine Oil and Filter
First up, if your car is from earlier than 2008, you should aim to change your oil and oil filter roughly every three months or 3,000 miles (∼4,800km). Many vehicles made after 2008 can safely make it six months or 5,000-7,000 miles (∼8,000-11,000km).
Some mechanics say you can change your filter every other time you change your oil, others suggest doing it every time. Refer to your owner's manual for oil and oil filter recommendations for your vehicle.
Engine Air Filter
Next, you need to find and inspect the engine air filter every three years, or between 15,000 and 30,000 miles (∼28,000-48,000km). You may want to shorten this interval if you live in a very dusty or humid area.
Some engine air filters are easily accessible, others are fairly difficult to remove and replace (Dodge Caravan, we see you). Locate yours, carefully take off the protective cover and remove the filter from the casing. Inspect the folds for debris and dust. Some engine air filters are washable, but most vehicles use replaceable varieties.
Engine Coolant Level and Strength
Your engine coolant level and strength is another important checkpoint on your vehicle and should be tested periodically. Some manuals recommend taking a look after 60,000 miles (∼96,500km) and then every 30,000 miles (∼48,000km) thereafter. Add some coolant if the liquid doesn't reach the "full" line on the reservoir.
Coolants come in many colors, the important thing to check visually is that it's relatively clear. If it's very foggy/milky, or if there are visible floating particles, you should flush your system and change the fluid.
If the level is good and the fluid is clear, your last step is to pull a little bit out with a baster, put it in a small container and apply a litmus test. If it comes back highly acidic, you should still flush the system, since that can result in corrosion and other damage to the cooling system.
Tire tread and air pressure are both important for vehicle safety. The commonly accepted measurement for okay or better tread depth is 4mm or more—roughly 2mm is the bottom limit for safe driving.
If you don't have a tire tread measuring tool on hand, you can use a coin for a rough estimate. Pressing an American penny into your tire tread should obscure part of Lincoln's head. If the top of his head is visible, you're due for an immediate replacement. In Canada, you can check with a Toonie (if the depth goes up to the bear's feet, you're in good shape, if it doesn't clear the silver, it's worn out) and in Europe, you can use a Euro (if the tire goes into the gold and almost to the bottom of the number, the tread is deep enough, if it doesn't reach the edge of the silver, it's time for a replacement).
Check the air pressure in each tire, including your spare. There's nothing worse than breaking down with a flat tire only to find another flat in your trunk. Use caution while refilling your tires—too much air in a tire can cause you more problems than too little.
Tires also need to be checked for the pattern of wearing on the tread. It's a good idea to rotate your tires roughly twice a year to ensure an even wear pattern through their life cycle. Excessive wearing on the inner or outer portions of your tires can indicate that you need to perform an alignment as well.
Turn Signals and Headlamps
Next up, check that all of your lighting and signaling mechanisms are functioning fully. This includes your front and rear turn signals on either side, your parking lamps, fog lamps, low beams, high beams, reverse, and braking lights. Quite the list, right? You can knock this exam out quickly with a friend or family member as a second set of eyes.
Suspension and Shocks
If you live in a town with brick roads or an area full of potholes, you may want to conduct a regular examination of your suspension system. This includes the front and rear suspension and shock systems, along with the sway bars that are located in the front. Examine these for cracks, broken bushings, or exploded canisters and replace as necessary.
This routine check on the list is something that so many drivers forget about, much to their displeasure later down the line. Your fuel filter prevents any debris that might be in a gas station tank (or your gas tank) from reaching your engine.
When the fuel filter gets too old, it rusts out, stops working, and eventually prevents your fuel pump from functioning at all. This will end up forcing you to perform a total replacement of your fuel pump and filter, which gets to be quite costly. Examine the fuel filter for rust and cracks a few times a year and change it at least once every 15,000 miles (∼28,000km).
Exhaust and Emissions Examination
A good place to wrap up your inspection is your exhaust system. To give it more than a cursory glance, put on some goggles and gloves and examine the pipes from the rear of the vehicle to where it connects with your engine.
Gently scrape away any built up rust to check for small holes, which can admit air that causes backfires in your pipes. Look for black streaks or marks near the connection points that could indicate gas has been escaping. If you see either of these problems, you may need to replace parts of the system for safety.