When the finish of your car loses it's luster, or when your finish is just plain finished, it might be time for a respray. In order to make sure your new paint sticks instead of peeling, and parts that shouldn't be painted aren't, these are the steps a good automobile body shop should follow.
The main parts a body shop should remove are the front windshield and rear window. This way they'll be no paint lines next to the rubber molding around the window. A good body shop will require that the windows to be removed as part of the warranty that you receive. Take a look at cars the shop has previously painted, to make sure of the quality of their work. If there are over sprays on glass, trim, or molding, it may be best to go elsewhere. After all, it's your ride, and you'll be living with the final results.
Sanding the car down to bare metal is good, but not essential. Body shops now use a chemical stripper that eats the paint right off of the car, but leaves the undercoating. The only parts that need to be sanded to bare metal are the bonnet, roof, and boot. These are the panels that are most likely to peel later. Proper metal preparation will prevent this, and if you receive a full warranty, it will cover peeling.
If you want to paint the car a different color, then be prepared to go all the way, and remove the engine, all parts from the engine compartment, entire interior, entire trunk, and a lot of other parts. The other choice is just want to paint the surface areas that will be seen. It will save you money, but will be obvious the minute you open the bonnet. A good body shop can work with your budget and still make the car look good.
If you want a bumper or front fascia painted, always remove the moldings and trim. Try reading the shop manual on the proper way to remove the item. The only type of body shop that will take the time to remove all of the moldings and trim and put them away in a nice orderly fashion is a custom body shop. These shops will totally take apart your car, rebuild it, and respray it whatever color you desire. They do custom work like graphics, pin stripping, metal flake, sparkle flake, or candy. These places will charge around $7000-$8000 for a custom paint job and about $3000 for a basic paint job. The wait can be anywhere from 6-8 months. But the superior quality of the work will shine for years to come.