definitely forward (at least when you first get on).....i slid an uphill rail for the first time not too long ago after getting real comfortable with flat ones, and the first few times i hit it with the same balance and fell backwards immediately. once you get on though you kinda slow down, depending on the consistency of the rail......if you are fine on flat rails just give it a try or two, i made it just about all the way my third try and greased it my fourth, and i'm not that great at rails at all, so you'll be fine
-Strode
Abba Zabba, you my only friend