General:
* Before
* Ahead
* Forward
* Prior
* Preceding
* Previous
* Leading
* Front (as an adjective)
More specific:
* In advance (referring to time)
* At the head of
* At the forefront
* Leading the way
Spatial:
* Forward
* In front of
* Ahead of
* Facing
* Opposite (in some contexts)
The best word to use depends on the specific situation. For example, "before" is appropriate when talking about time, while "in front of" is better for physical location.