Do plenty of research on models you like. Google common problems with the model.

Mileage, people sell cars at 50k, 75k, 100k etc. Anything over 50k will either need or has had a major repair. Don't buy something that will need a major repair in the short term.

Once you find something that you feel good about, ask if you can take it to a mechanic for it to get an pre sale inspection. You may spend a few hundred but it may save you thousands.

Sales guys will try and get you through a four square technique. They make you say yes three times ( like the color?, like the stereo? Drives nice right? ) then pass you from sales, to finance, trying to make you feel like you can't back out.

Remember you can always say no, walk away and go else where if you don't like it.

Banks won't finance too low of value. Sometimes buying from a private buyer will often give you the most options to negotiate. Don't be afraid to negotiate.