Agreed. Seeing how I probably have more painting skills than beerman or those others listed, I am more qualified to answer this. I myself have painted many bikes, and will break down the process for you.
Remove all stickers from the bicycle, And Completely disassemble the bike.
Get some GOOD paint thinner as, most bikes are powder coat, and powder coat is a ***** to remove.
Afterall the paint is removed, whiped the fram with a damp rag, an whipe off anything that'll screw up the paint. If there is rust you may want to take a paice of sand paper and sand it off.
After the bike is prepared primer it, with atleast two coats of primer.
Step five after the primer has dried paint the bike with the paint you have selected.
I am hardly qualified for this one anymore as it has been 10+ years since I've repainted my bike. Almost every DIY paint job looks good, but I have yet to see one that is close to the durability as powder coating.
You have to be pretty serious to powder coat though.
I used paint stripped from the local hardware store to get the old paint off my frame. Usually took all day just to make sure I got it all off and then to sand down what I had not been able to get with the stripper. Then I completely cleaned the bike off and let it try.
From there - I really did as listed above and went with a couple of coats of primer and then painted the frame. I am not sure, but I believe it is possible to get much higher grade paint more easily these days. Automotive paint? Not sure, but you do want something that will be durable.
If you do want to have your frame custom powder coated, call some motorcycle repain shops in your area. Especially ones that do custom work. They can put you in touch with powder coaters - but plan on spending up to 100 bucks for your frame to be painted this way. On the other hand, my friend had his done and rode the frame for 4 years. When he stopped riding it, he pulled it apart and cleaned it up and it looked like the day he got it except for a couple of slightly dull spots. Pretty durable stuff.
Mude, take the advice of the Fire Chuck over us. Because at 14, he must have more experience than the rest of us. If you have rust, you should use a chemical remover, such as Naval Jelly, which will completely remove all the rust, without taking off extra metal. Before primering, scuff the frame with a Scotchbrite pad so the primer will stick better. If you know anyone at a body shop, or car dealership, you may be able to have them paint your frame when they're spraying a car. I had a friend at Toyota that got a sweet Supra pearlescent white paint job dirt cheap. Clear coat included.
If you're doing this at home with spray cans, there's a few things to keep in mind. You'll need ventilation, so you're not huffing paint. At least do this with the garage door open. Temperature is important too, so do it at the hottest time of day for best results. If your garage or workplace is dusty, you can even spray a light mist of water on the floor before you start, so that you don't churn up dust. Go search the road and MTB forums also, as there's lots of tips on painting. Powder coat is the best option if you're keeping the bike a while.