As Dragon J stated different people have different ways of doing things according to their skill and comfort.
The proper way to paint a vehicle is section by section to minimize the chance of mismatching sides or parts. What I mean by section is the three parts of a vehicle: front (fenders, hood, etc) middle (doors, roof) rear (quarters, trunk rear). Then of course its sprayed from top to bottom. Always spray the top of each section first (IE hood, roof, trunk) so you don't lean into the fresh paint if you do the sides first. Painting a vehicle section by section will help a great deal with any paint, but expecially candies. Do one coat on each section then by the time your done with the rear your front will have probably had enough flash time to add the second coat. If you paint a vehicle by sections you will have a smaller chance of visable color difference because its distributed over a larger area. Not only will the the color be easier to match, but the drying time of the paint will help blend the color more smoothly. If you spray a car side by side, by the time you finish one side and start the other the previous side coat will have had time to flash and their will be a noticable color difference do to the time allowed to dry before the other half was painted. If you spray a whole side then the other you have a greater chance of developing a soft line down the center of the vehicle. Thats the proper way for beginers or any painter, but after years of painting each painter developes his/her own style.
Dragon J is again correct. your spray gun should have a adequit spray pattern to spray large areas, but the gun should never be closer than 6-8" from the surface being sprayed. Also keep the gun straight, never bend your wrist, keep your wrist straight, if you run into a contour keep the gun parralell to the surface to prevent paint buildup (runs <img src="graemlins/drunk.gif" border="0" alt="[drunk]" /> )
I of course have my own style just as dragon J. I still spray by section, but I have very long legs so I can cover a section in half the time of a normal painter. I also do the spider legged spray dance. I can cover an average sized car in 8-15 before another painter because of my long legs and years of gun-time. Once you do it a few times you learn what to do and what not to do and where you can develope your own way of doing things.
Candy is not for the cheap or faint of heart of unexsperienced. Its not forgiving and if you mess up you have to take it all off and re-do it. Have fun, take your time andd if you need more help feel free to ask.