I looked for my Mazda3 for over 2 months. Here's what I kept in mind:
1. Have someone who is knowledgeable about cars and repairs as a contact to ask specific questions.
2. Never bother looking at a car with a rebuilt or salvaged title.
3. Ask the owner where the car was serviced, how often, and if they have service records. You will get a good idea how well they took care of it.
4. Ask if any body work has been done and why.
5. When looking at a used car, look for discrepancies in paint or parts. If there is paint that doesn't match up with the rest of the car, then you can tell there has been work done that involves replacing major parts.
6. Check the oil. Pull the dipstick out and check how high the level is and if the oil's clean. Changing the oil is a major factor in the life of a car.
7. Do research about the specific car model and see if it has any model-specific repairs. For example, Honda Civics older than 2000 have timing belts which need to be replaced every 60k miles. The newer models have timing chains which don't need periodic replacement. For my Mazda3, the big thing was that it can wear the wrong type of tire quickly (as fast as 1 year). I put on Bridgestone tires to ensure tire maximum lifetime.
8. If you have a motivated seller, they will be willing to work with you on the price if you find any repairs that need attention. The guy I bought my car from took off $800 right away because the car needed new tires, had cosmetic dents and scratches, and needed new brakes pretty soon. I also asked for another $150 off to have the car detailed and buffed.
After my car buying experience, I would be more concerned on getting a very reliable car than getting an amazing deal. There are pretty good deals all around; they're good only if the car runs good and has been kept it good shape.