Is there a site glass? It's usually on top of a cylinder called the receiver dryer. It's also usually dirty! Clean it, then start up car. Run A/C until it is cycling. Watch the site glass (use a flashlight) and right when it kicks in, the bubbles should disappear. If they disappear and should stay gone until the clutch turns off again. If there are still bubbles, the system is likely low on refrigerant. Have it added professionally, the new systems take all of it out, clean it, and put in just the right amount via computerized charging station.

Things you can check yourself:
-Is the condenser clean? (It looks like a little radiator in front of the radiator) Clean it with hose; don't use too much pressure.
-Is the drain plug clogged? On a humid day, look for water dripping out (after A/C running full blast for a few minutes) of a hose on the passenger side. If it's really slow, some compressed air can clean it out, or even a q-tip. If there is water on the floor of the car on the passenger side and none on the ground, then the hose is completely clogged. (Clear it the same way.) It may be harder to identify.
-Turn off the engine, let the car sit for about an hour. Try turning the A/C compressor by hand. (Not the belt part, the part that stays still when the compressor is cycling. Watch it while it is running to identify this part). It should turn without much difficulty.
-Does your "Recirculate" work correctly?
-Is your heat stuck on?

All other tasks require a professional.
Good luck!

Nate