First off, a great landing starts off with a great traffic pattern and a stable approach. If you're floating that means that you're off speed (too fast), too high coming over the threshold, and/or shifting your aim point. Your instructor should be demonstrating landings and giving you tips on power settings for different landing configurations. I somewhat remember out of the back of my mind that 1,400-1,500 RPM in a C172R with full flaps pretty much held you on speed (65 kts). Power pull is also important (as in when you pull the power). It should be smooth and mechanical every time. With a no-flap landing, you can pull the power a bit earlier because of the decreased drag of a clean airplane. You should be coming over the threshold at about 50 feet. Don't be afraid to pull the power earlier. Remember that you can basically pull the power to idle on a 172 or Cherokee/Warrior at midfield downwind and make a normal landing. Power and altitude provides a new pilot comfort from the inevitable rough landing and so floating is quite common. Ground rush can cause you to tence up on the yoke ever so slightly, which in turn shifts your aim point. Landing is the hardest thing to teach and it requires a lot of muscle memory to master. I wouldn't get discouraged. I've had students that had extended growing pains with landings only to have something "click" one day and they were landing better than me.