If your friends stick their feet in your spokes, there isn't much I can tell you that will be of assistance. Perhaps, "Get some new friends"?
More advice? Watch out for Belgian cross fans, square edged walls, rails, and ponds. And you might want to just think about wearing a helmet. And I don't have a clue about how you avoid this stuff.
You may want to think about not jumping your mountain bike over the Peloton in the Tour de France... the Gendarmes get really funny about things like that.
And last thing, if you happen to see a motorcycle-borne camera during your pathetic citizens' race, do not mug at the camera in lieu of keeping your eyes on the road.