My 2 cents. At least for the Lake and Skimmer. Attitude sets the airspeed and power controls rate of descent. Before we get near the water, or on the way to the water, I have the student set up the correct attitude using visual references like the horizon and longitudinal reference points. Nose just slightly up from level, using about 18 to 20 inches of manifold pressure. Basically, slow flight. Then we hold the attitude and airspeed and reduce the power slowly until we get a 200' per minute rate of descent. Once that stabilizes we check the manifold pressure and remember it. Most Buccaneers and Skimmers end up at close to 58 mph and 16 inches of MP. This last figure will change with load and density altitude. For the actual landing, we descend without power to just before the last visual reference, then add power to the known setting, then adjust the attitude which adjusts the airspeed, or do it simultaneously. But NEVER adjust the attitude first. At this slow airspeed, if we bring the nose up first, we are immediately going to lose airspeed and it is already slow. Power in first to prevent a sink rate from starting. It takes forever to fly out of a sink rate at reduced power. It is the last thing we need to have happen when we don't know where the surface of the water is. Everything should be set up before we cross the last visual reference. There have been many aircraft sent to the bottom because they were out in the middle of a large, glassy lake attempting to set up a glassy landing with no last visual reference at all.
Once contact has been made do not make any power changes until you are absolutely positive you are on the water and you will feel it rather than see it, since any spray is far aft. The best indication is the airspeed dropping off due to more and more friction on the hull which is displacing more and more water. Remember that until this happens you still have flying speed. With the pusher configuration of Skimmers and Lakes one must also be careful not to reduce the power too rapidly where the sudden lack of nose down thrust changes the attitude to nose up and you find yourself flying off the glassy water with no power and deteriorated airspeed and no idea how high you are above the glassy surface.
One little trick that I have never really had the guts to try is using the little mirror on the wing float - it is there to check where the nose gear is (up or down), but you could if you concentrated hard enough watch the reflection of the hull on the glassy water get closer and closer. It is smarter to look out at the horizon, though...and the gauges.