Step 4: Priming the frame and other parts
Now for the fun part get out the primer. Read the directions on the back of the can, and kick on the fans if you are working in an inclosed area like me in a garage, with the door open of course. No seriouslly do it, the directions on the back of the can are there for a reason(and are often quite helpfull), and the fans are a must, paint fumes are nasty and if you start to feel sick or light headed while working stop and get some fresh air.
The best way to spray paint with cans is to, hold the can about 10 inches from the subject and to make long even passes, also it is a good idea to go and do all the junctins of the frame tudes and the bottom bracket area first, as they are the hardest to get and easiest to get runs in if you over do it. Another good idea is to use many light coats instead of one or two heavy coats.
With the primer what you are attempting to do is cover the areas where you sanded alway rust and also to fill in and even out the light gouges and imperfections in the old, worn, paint so that you have a nice ever surface to paint on.
After priming I like to lightly sand the frame, with either 220 grit wet/dry, to keep the paper from clogging, or also a red scotch brite or 00 steel wool pads, which do not seem to have the clogging issue. This gives a real nice smooth surface for the paint to adhear to.