First step is do a little body work and fill any obvious low spots. Then prime the entire car, and guide coat it. Then the fun begins... blocking the whole car finding more low and high spots that weren't that obvious. Fix/fill them with some glazing putty. Prime and guide coat and block sand again making sure all panels are flat and ready for paint. Wet sand car with 400grit, and you're ready to lay out the top coats. Many hours go into prepping a car for paint.
It's alot of work. Your paint job is only as good as what's underneath. Do not attempt to paint it without doing the necessary body work and blocking everything flat. New glossy paint with magnify every imperfection. I suggest looking at alot of youtube vids about apply body filler, primering a car, block sanding, & wet sanding. There's lots of information out there, and it'll give you an idea of how much work will be involved.
Or you can take the easy way out and just paint over what you have, but believe me... you will not be happy with the end result.
