O.k. I took autobody in college! I think if it's a car you care about get it done proffessionaly. If it's one you don't have fun invite friends and drink lots of beer (canadian beer of course)! Just make sure you mask (cover the windows and trim) before you start drinking. This is important. If there is body work get it done for you. If you don't care then start here.
Get a real car soap not dish soap or cleaner. Wash it well!!!
Go to an autobody supply store and buy yourself a fine grade sand paper for wet sanding! Believe it or not Scotch Brights work well and are cheaper! Also save your hands and buy a sanding block. Not for use with Scotch Brites. Buy a couple because your going to convince someone (more being better) to help you if you buy beer (see this is were the beer comes in). Just attach the paper to the block grab a hose (this is wet sanding) and where the water is coming out do circular motions and work your way down the car. You can see the shinny paint ( clear coat) dull. This takes a while and therefore lots of beer! Just dull it up don't remove paint. Watch out for your trim .sand paper marks look like s#@t! You are scratching up the paint so the primer has something to stick to. Dry it while drinking beer. Mask all windows and trim with tape ( not duct tape, masking tape that's why it's called masking tape. Make sure you aren't to drunk for this step because you don't want paint on your windows, lights, etc. Buy yourself a spray gun nossel that fits the top of a spray can. It's just a fancy spray can handle and tigger. Buy a suttable primer for the color you are going to paint it. I suggest you paint it because primer is not meant to be exposed to moister or dirt. Start on the roof, do the entire roof then the pillars, then half the hood( watch out for overspray on anything you don't want spatter painted. While drinking beer of course! You can cover the tire with an old blanket. From the hood to the front. Down the fender across the door trough the quarter pannel across the hood (on vertical surfaces top to bottom 30% overlap) on flats bumper to window and back) down the back don't spill beer on the paint, across the next quarter, door and fender and accross the rest of the hood. Make sure you have enough paint and beer! Doing it all at once makes it look better! Step back and admire the work even if you f%#ked it up you will be so drunk it looks good! I suggest doing it at a cooler time of the day so the paint won't dry as fast! Don't do it at night there is to many bugs to ruin the smooth surface. Drink lots of beer until it drys probably the next day! LET IT DRY before taking any masking tape off it will peel new paint right a long with it! Wake up and unwrap it. Repeat with paint and beer if you want color! Good luck!
Scotch Brite is a registered trademark of 3M!