Painting a frame will be like painting anything else, aerosol is best, slow and easy wins the day.
good primer, spray it on and let it dry, using a fine wet and dry wet with water, something like 1200 grit, give it a light sand, another layer of primer sanded again lightly to smooth the layer.
lay down a thin layer or colour, sand with 1600 grit also wet with water to smooth, lay down another 2 coats and rub back again keep the coats thin and apply one more do not rub this back, leave the frame to dry for at least 48 hours, and then apply a coat of clear lacquer in a dust free environment and then leave 72 hours to harden properly.
Thats how you will get a decent finish to warrant doing it diy, id suggest powder coating though, i have just had a quote of £48 to blast and powder a frame, the finish will no doubt be better and much more durable.