The first rule is make sure the rear derailleur is adjusted correctly before adjusting the front derailleur.
There are three adjustments that you can do on the front derailleur:
- Clamp Position
- Low limit stop
- High limit stop
Here you can adjust the height of the derailleur, normally this is recommended as a 2mm clearance between the bottom of the outer cage and the teeth of the large chainring.
Picture from bicycletutor.com site
You can also adjust the rotational angle of the derailleur.
Picture from Parktool site
The Limit stops are for adjusting the inward and outward travel of the front derailleur. Limit stops are marked "L" for Low and "H" for High. The L-stop will stop the movement of the derailleur toward the smallest chainring. The H-stop will stop the movement of the derailleur toward the largest chainring.
There is a good guide on the Parktool site that gives a lot of detail on adjusting the front derailleur.