Diy paint/high school budget

Hey guys I'm wondering if anyone's painted a car themselves. I went to lowes and bought some gray paint. It's rustoleum in a gallon bucket. I have spray guns and I've painted wheels and all kinds of random things but never a car. I wish I could afford a better paint job but Im on a highschool budget so im doing what I can with what I have. If anyone has any advice for me let me know. I don't know what kind of primer to use. If you have any advice let me know thanks guys