Topping off your gas tank (when the pump shuts off and you give it another quick pump to make sure it’s full) can ruin a device called the EVAP purge valve. Topping up the tank will not leave enough room for the gas vapors to get into the charcoal canister. Instead liquid gas gets in there and it can clog up the EVAP lines, which can cause the gas pump to constantly shut off before the tank is full. These devices are expensive.
If you constantly turn your wheel to the point where it cannot turn no more, and hold it in that position (most of the time this is done in parking lots, u-turns, etc.), your likelihood of busting a power steering line is quite high. There is a noticeable audible sound when you do this, and when the wheel is cranked all the way it prevents the power steering system’s fluid from reaching the gearbox because the flow is blocked, thus creating backpressure in the system. First part to bust in this situation is the pressure line to the gearbox.
Have your side view mirrors angled so that you can see your car in them. There’s no point being able to see cars behind you if you have no reference point to where your own car is.
Don’t ride on the clutch. Your inexperienced driving with the clutch partially engaged will wear the diaphragm before you wear the asbestos of the clutch packs. In a nutshell, if you’re coming from a stop, obviously feather the clutch to get going. If you’re in 2nd or above, it’s either on or off, so get your foot off the clutch.
Get an alignment if you curb your wheels (hit a curb). Also if your steering wheel isn’t perfectly straight, get an alignment. In both cases, if you don’t get an alignment right away your tires will wear funny and be worthless.
Parking outside in the sun/exposed to the elements regularly. People ask me how it is my cars that are over 10 years old look new. Part of it is because I park in a garage at home (as opposed to accumulating boxes in my garage) and park at a parking garage at work. Sun fades paint, peels some clear coats, loosens plastic fastenings, releases glue (causing issues like drooping headliners), and eventually leads to faded, peeling, and cracked interiors.
When small things don’t get fixed, it ends up costing much more to repair. For example, I once had a car come in with a really bad ball joint. The customer declined repairs and went on their way. I got a call 10 minutes later saying the ball joint let go and it was getting towed back to the shop. They ended up having to replace the ball joint, along with the CV axle, and the wheel bearing. This ended up costing nearly 3x as much as if they just replaced the ball joint in the first place.