Not Using the Parking Brake
The parking brake is not optional equipment. It locks up the wheels so the car doesn't roll downhill. It also prevents stripping the parking pawl in the transmission when in "park." The car is not meant to be "held" by the transmission; that is what the parking brake is for. Remember to release the brake before driving away.
Not Coming To a Complete Stop Before Shifting Into Reverse
You strip the gears and bands in the transmission when you don't come to a complete stop before shifting into reverse. Eventually, you won't be able to shift gears because they will no longer have teeth to mesh, nor any bands to apply tension to hold all that force in place for propulsion.
Forgetting To Change the Oil
While this engine clearly had issues beyond running low on oil, it is clear that lubing up is important. The engine has metal pistons with round metal rings that slide up and down inside the metal cylinder. If oil is not maintained, the metal-on-metal rubbing can eventually lead to some major issues.
Pressure Washing The Engine
Power washers supply extreme pressure to everything you spray with it, including those closed modules where expensive electronics are housed. A clean engine is nice but at what cost?
Starting Your Car The Wrong Way
Don't forget to turn your AC off before staring your car; AC is connected to the serpentine belt, so it requires the engine to work a little harder when it is left on.
Ignoring Your Car's Sounds
Squeaking brakes and scraping metal when braking usually means metal to metal contact, and that your brake pads likely need replaced. If you ignore that sound for too long, you will likely wind up destroying your rotors, causing a more costly fix. Worst case scenario, your brakes fail to engage properly causing an accident.
Letting The Interior Go
Food and drinks can begin to rot in your car just like they do in the refrigerator. Those empty containers on the floor and the junk left in them WILL rot and stink. Eventually, you won't be able to get rid of the smell.
Running Your Car Down To Empty
You probably didn't know that the fuel in the gas tank actually helps cool down the fuel pump. Even if you believe in the "Buffer Zone", don't rely on it; you may think you are saving money by fueling less often, but really you are just setting your car up for bigger issues. Try to keep your tank at a 1/4 or more full to avoid fuel pump issues.
Fluids are supposed to stay IN the vehicle; that's their job. If you begin to notice fluid leaks under your engine, you should probably get them checked. You should know the various colors and where they belong to save yourself some hassle. Coolant can be green or orange while Transmission Fluid is generally red. Oil is a caramel color, but turns black when it is used. Brake and Power Steering Fluids are both clear.
Ignoring "Check Engine" Light
This light means that there is an issue with the computerized controls somewhere. By ignoring this light, you are potentially harming the internal control system of your car--you know, the one that controls EVERYTHING--and even possibly damaging your catalytic converter.
Not Flushing Coolant
Engines get really hot, and the coolant system is set up to keep the car from over heating. If you never flush your system, or attempt to refill it with just water, you will likely wind up with a clog, rust, or worse.
Driving Past Attractive People
Regardless of your preference, pretty people have a tendency to distract drivers who forget they are behind the wheel of a car. Because of this distraction, people suddenly find themselves in the back end of another vehicle. Keep your eyes on the road and remember, you are operating a several thousand pound vehicle which qualifies as a lethal weapon. Your car will thank you, and so will the unsuspecting public.
Riding The Brakes Down A Hill
Don't ride the brakes, or rest your foot on the pedal, when going downhill. If you do, it could wear away the brake pads faster than you intended, and when you finally need the brakes to work, they may not. Brakes may be cheap, but there is no reason to wear them out for no reason.
NOT Seeking Out Advice From Trained Professionals
In an age when you can learn anything you want to online, whether true or false, it is important to double check what you learn online with trained professionals. So befriend a mechanic and your car will last for a long time.