Help on buying first car?

Hey everyone, so I'm just looking for some help on how to buy my first car. Basically, I'm 20 and need a car badly. I want to buy a used car, something cheap like $4000-$7000. Can anybody give me advice on this, such as how much would the salesman cut the price if I haggle with him, what questions should I ask him, what should I look out/be weary for, what are some common mistakes, whens the best time to buy a used car, etc. Thanks everyone!