I fish a large reservoir as well. A topo map helps me a whole lot. Finding the creek and main lake channel and places where they touch points, bluffs, and etc. has proven to be quite successful. However, spots on the map are much larger and harder to cover once you get out there on the water. If you don't already own a boat and a good sonar unit, I'd save up and buy them as soon as possible.
Aside from a topo map, it's good to ask some locals. Good Luck