I fish from a kayak and had to learn to cast siting down. I practiced actually siting on the ground and casting (my kayak sits even lower than a canoe). Concentrate on good technique for shorter to medium range casts. Long casts can be really difficult. Two things to remember is that with the stealth of a canoe or kayak, you can usually get closer to the fish and if you are on open water, try to position yourself for downwind casts. One other thing that I have found is that, due to the siting position, I can actually get more power from a backhand cast.