Originally Posted by SouthernMike:
Track before everything. Get your track in place and wired, then run trains for a while to make sure the track plan is what you want it to be. Then start scenery. You don't want to be a good ways along with your scenery and then decide you want to start adjusting your track plan.
EDIT: Just re-read your question. If you are talking about grass paper then you will want to put it down first. When I initially answered I was thinking of ground cover or static grass type of scenery.
Thanks. I meant to add that I was talking about ground cover.