sorry it took so long to reply. it really depends on how bad the original paint is like say you have chips you might want to featheredge the chips out and all. thats when you basically just sand the chip out and create like a circle and feather it out smooth into the old paint. if the paint dont really need to be fixed anywhere like that. you can just 320 grit the whole car down. but say you feather edged the chips out primer those spots up hold your gun back a little to get a nice film build, and let it set up and dry good. if your gonna use dupot paint the URO primer is nice had a nice build i liked it alot. runs like $30-$40 a quart and then $20-$25 for the activator i think its a 3 to 1 mix but if you dont use as much activator you can keep the primer thick for good builds more activator you use when you stir it you will see it make the primer thinner. from what teeto said is right. from body work up the different grits and all.
use 80 grit when your sanding body filler get good filler if you have body work not cheap bondo crap get like evercoat.
then 220 grit after the 80 grit if you just primer over the 80 grit then sand it if you bust thru the primer when sanding with a finishing grit like 320 or finer 400 600 etc, and you bust thru the primer when you paint you'll see the 80 grit marks show up in the paint
so 220 after you 80 grit down your body work then you should throw a couple nice coats of primer with nice builds. then da all the flat area down with like a finishing sander. find these cheap at like harbor frieght etc. just like he said dont sand by hand your hands also not flat if you ever have to sand by hand use the palm of your hand its flatter. then you can finishing sanding your car with say 320 grit, you can step it up to 400, 600, 800 etc after the 320 but really thats just more work for yourself, i mean the finer the surface the better the paint will look. you can probably go over it dry with 320 then wetsand it lightly with 320 with water on it let the paper do the work. then your ready to shoot it. depending on what color your gonna use since your gonna use dupont get a value shade sealer. They go from VS1 to VS7 basically VS (valueshade)1 is white then it goes all the way to VS7 which is there darkest, spray the sealer before the base helps alot. so lighter colors such as white use vs1 darker like blacks, blues,etc use vs7. ask the sale rep which VS goes with that paint they would know. Throw down like 3 good soild basecoats. Watch the paint as it goes on keep the motion even release the trigger as you stop on both ends of the stroke. try to keep the same distance so you prevent orange peel. If the base looks like its orange peeled you can hit it with some wetsand paper and just spray back over the base again. Let your basecoats flash off wait time usually on painting condition usually like 15 mins in between coats. Then throw like 2 coats of clear on it and your done. Same steps with the clear. look on the back of the cans and it will tell you how to reduce them etc. Spend the money get the green 3M tape for making the car and a roll of good paper not newpaper that will blead thru, so yo dont have to scrape paper off your windows when your done. Keep the floor wet too to keep from dust blowing up. Im guessing your doing this in your garage cause if you had a paint booth you woulnt be asking these questions. Get yourself some tack rags. Get some dupont cleaning prep solvent too to wipe the car down before you spray it. then tack rag it in between coats. use a overlap fashion. take the tack rag say start in the middle/back of the hood drag it down to the front of the hood move your hand down maybe 2 inchs when you reach this point come back up in a overlap fashion same thing when you spray the basecoat overlap the last line you spray. If you tack rag it in between coats it helps keep the dust off alot. If you get dust you will see it in the basecoat just knock it off with some like fine 1500 grit paper and spray the base back over it. now right before you clear it tack rag the whole car again id do it twice to make sure there isnt any dirt on it at all. so when you clear it you wont have dirt under the clear. another thing is blowing the car off too make sure you blow it off outside of where ever your painting it you dont wanna have dust flying around when your painting it. pop the hood blow under there inside the car all the cracks, everwhere before you pull it in there helps alot. It would really suck if you didnt do this then say when your painting and your spraying the door and you had dirt in between the door and fender that blew out when your painting your gonna be pissed then when it gets all into the base. If you can spray primer out the can pretty decent same way with a paint gun make sure its atomized enuff and shoot it. dont be scared practice on something small like the spoiler first if you are if you mess it up. sand it down and paint it over. you can do this off the car ya know? better then rushing in and painting the whole car with no experience at all. guess its better to mess a spoiler up then the whole car ya know. And actually if you have a LX you would probably wanna paint the spoler off it anyway so you can spray under the spoiler too if your doing a complete color change. then you can do all the steps on the spoiler. Primer,sealer,sanding, base, clear, etc. Just remember when you activate the sealer get cups so your not activating everything activate only what you wanna spray. and get a decent guy too like the other dude said SATA or a DEVILBISS. You can find these on ebay cheap. GOOD LUCK this post is long i know but takes forever to tell all the steps. message me back if you need anymore info. see ya