I always had a problem of flaring too high, which bleeds off the energy and then BAM. You're on the ground, but it's more like getting shot down than landing.
The trick is to control your airspeed on the approach, if you've got that nailed, then you're about 80% there. If you come in too fast, you're gonna float for days, if you come in too slow, assume the crash position. Does the 150 have 30 or 40 degrees for flaps? If 40, try just using 30. I used to use 40 on the 172N, and I hardly every do that anymore unless I need down NOW. If you've got good airspeed control and a good descent rate, it's conceivable to only use 10 or 20 degrees of flaps. You might float more that way, so know your runway length.
Ditto what everyone else said about looking down the runway. Use your peripheral vision as well to get a feel for how high you are. Like Tony said, the trick in the flare (which was the hardest thing for me personally to learn) is the finesse of pulling the nose up. Too much, too fast, and you're gonna come right back up again and bleed off your energy and airspeed. Not enough or too slow, and you get the nose wheel through the floor (thanks, Lindsey. I like that one). The trick is to pull it back and a slow, consistant rate and let the airplane sink to the runway. One way to do get the feel of this is to do a sort of soft field landing/low approach method. Come down like normal, but kick in a little power during ground effect. Then play a game where you try to keep the wheels off the ground, but don't climb. Once you get that, do it without adding power.