The paintjob will only be as good as the prepwork. Sandpaper is good, but you'll also want primer to help the new paint adhere to the frame as well. A very careful job of degreasing the frame is also important.

1) what type of paint (brand and paint base type (enamel, etc)) are you using?

2) what grits of sandpaper are you using?

3) how much time are you willing to put into it for a quality job.

Since I never tire of putting up pictures of my paintjob - here's one I did with just a few rattle cans (well, like 6 cans) and plenty of time and effort:



Rough sanded the frame down to smooth out scratches in the original paint, and help the primer adhere. Then did a first coat of primer, let it dry, then a second coat. I then wet sanded the primer before shooting one more coat of primer to fill in any thin spots. Final very light wet sand on the new areas. Then put down 2 coats of color before another wetsand. Then 2 coats of clear.



The paint I used isn't the most durable finish out there, enamel is probably better, but takes longer to dry and cure. Best last bit of advise I can give you, after finish painting it, let it sit for a week at least. Don't even think about putting stuff on it till a good 7-10 days, more if its cold or damp.



More pictures and such on my website (Barracuda Mk.I link in sig). Here's also the link to the thread I had going when I was doing this build: http://www.bikeforums.net/showthread.php?t=148985