I would wash them, then sand them with some 180 or similar grit sandpaper. Then wipe with some acetone.
After cutting you're fiberglass to size, I'd mix the resin and brush a coat down prior to laying in the FG. Then lay glass, brush on to fill fiber and remove excess. I'd start small and do one gaunt at a time, and mix more resin for the next. Sucks to get caught up with it kicking off on the cure.