I tend to buy older cars (100k miles or so on them) and drive them to about 250k or more before I get rid of them.
I personally am not anal about things like oil changes and such. As long as the engine has roughly the right amount of oil in it, it’s going to be fine. I actually end up going a bit more between oil changes than the manufacturers recommend and I’ve never had a problem because of it. To prove the point, I even stopped doing oil changes on an old pickup truck I used to have (it was starting to rust apart and I wanted an excuse to get rid of it). It ran for 60,000 miles and 5 years without an oil change, never leaked a drop of oil and I only finally junked it because of body rust (which I could have fixed but by that time I was just really tired of the old thing and wanted to get rid of it). It never had an engine problem at all. Of course, I’m not recommending that you do the same, I’m just pointing out that oil changes aren’t as important as most folks say they are. Stick to the maintenance schedules in the owner’s manual and you’ll be fine. Don’t let the oil change places talk you into shorter intervals between oil changes like it is somehow better for your car. It’s better for their profits. It doesn’t really do much for your car.
While you don’t need to be anal about regular maintenance, you do need to be anal about any other mechanical issues that come up. For example, if the CV boots get cracked (common as they age) this isn’t something that you want to skimp on and forget about. Do it sooner rather than later, since if dirt gets into the CV joints it will cause them to wear out fairly quickly. Also, something like a radiator leak will cause the car to overheat and can cause major damage to it, so you want to get something like that fixed ASAP as well.
And do be anal about keeping the tires properly inflated. Rotating tires helps distribute the wear, as was already mentioned. Keep up with front end alignments. If you notice the car starting to shake or shimmy, get it aligned soon. A car that is out of alignment will wear out tires quickly.
The biggest thing by far though is to drive the car gently. Jackrabbit starts and hard accelerations will wear out a car very quickly. Try to keep the engine RPMs down low. A car that is driven hard isn’t worth much after 100k miles. The same car driven gently can easily get you past 250k. I usually end up getting rid of cars because they are rusting apart rather than because of some mechanical issue. All the regular maintenance in the world can’t prevent the damage caused by hard driving.
Put in exactly the octane that the owner’s manual recommends. Octane doesn’t equal quality. Octane is a rating of how much you can compress the gasoline before it spontaneously explodes. If you put in too low of an octane, the gas can explode before it reaches the proper point during the engine cycle when the spark is supposed to explode it. This is very bad for your engine. Putting in higher octane than recommended just wastes money using gas that won’t explode at compressions your engine doesn’t reach anyway. You won’t get better gas mileage. In fact, on some cars, you can get worse mileage with too high of an octane since many higher octane fuels burn a bit slower and this throws off the timing in the engine a bit. Modern cars have knock sensors which will prevent you from doing any damage to the engine if you use too low of an octane, but it still isn’t good for your engine. Use exactly the octane recommended in your owner’s manual. Do not use higher or lower.
Also, if your car is a daily commuter (as most are) try to fill up at exactly the same gas station every time. Have the fuel filter checked during regular maintenance. As long as the filter isn’t getting clogged, keep using that gas station. If you have problems with the fuel filter getting gunked up, switch to a different gas station until you find one that has clean gas and clean tanks.
Just my 2 cents.