If its a decent motor then get someone to do it for you!
Otherwise, preparation is key!
The more work you put in before you even pick up a spray gun the better the finish will be.
You will need to give the existing paintwork a quick sand with wet and dry paper to give the new paint a key.
Secondly, when you start spraying, if you have a garage, clean it out, thoroughly, you want to remove as much dust as possible, then get it warm inside. Get the car in then get it cleaned with cellulose thinners, to remove any dirt or grease on the paintwork.
Mask everything up you dont want sprayed.
If your spraying it yourself and your not put off by all the work you'd be doing then hire a compressor and spray gun, dont attempt it with cans!
I cant give you advice on spraying other than use even strokes, dont stop in one place for too long, and additional coats is better than trying to put more paint on too quickly. Oh! and get some practice in first!
The more coats you put on the deeper the paintwork will look, ie a better shine!
Once your finished spraying you'll end up with a orange peel finish which will need wet sanding to flatten off the paint, not too hard though!
You'll end up with a matt finish which will then need to be covered in laquer to give a shiny finish.
Seriously though get some one who knows what there doing to do it!
I did a Fiesta about 6 years ago and it took me 5 weekends to do it to my satisfaction. 1st weekend to remove bits like bumpers, decals, etc 2nd weekend to prepare (sand and mask up), another to clean and spray the main paint - 4 coats and the last two to sand, clean and laquer the car. Thats plus another odd evening to put the decals and bumpers back on.
mike