One focus for me when playing congas is to have as crisp tones as possible. Since producing conga tones requires the hand to move to varying positions on the drum, I like to practice moving between tones to practice my accuracy.
Sometimes these changes in hand positioning can be very subtle. For instance, to produce muffle strokes, my wrist is parallel to the surface of the head when my fingers make contact and stick to the head. But with open tones, my wrist is relaxed and falls below the rim edge when my fingers make contact with the head. Other movements require my arm to place my hand toward the center of the head, like for bass tones and palm-finger strokes. The challenge there is to move from the center strokes to the edge strokes (slaps, open tones, and muffled strokes).
Here are some combinations to help hone your accuracy.