Approaches by the numbers...
Hi TailDraggin,
You mention coming in too hot, porpoising and running off the end of the runway.
I think that Unstable is right on the money. You need to learn to fly the plane slowly. All of the things that you mention are symptoms of flying the airplane into the ground with too much airspeed.
When I teach landings, I recommend focussing on attitude. Specifically, you want to pay close attention to the pitch of the plane. Once you make the turn from base leg to final, the nose of the plane should never point down at all - even a little. It should always be either level or nose up. If you find that you don't descend with the nose level, or you climb with a slight bit of nose up, then you have too much power.
In my opinion, "elevator" is an unfortunate name, because it doesn't really control whether the plane goes up or down. Rather, it controls pitch. Throughout all the things I recommend below, concentrate on using the elevator exclusively to control pitch, and not altitude. Getting the hang of this will cure your porpoising.
Also, I'm assuming that you are not having any problems lining up on the runway, so I'll recommend an exercise to learn to fly at approach speeds. I won't bother to mention lining up on the runway and stuff.
Take the airplane up and practice some slow flight, per Unstable's suggestion. Then get into the pattern and do some flights (at a good comfortable altitude) over the runway. On each pass, keep the pitch such that the nose is level with the ground and reduce the power each time around. As you reduce power, you should notice that you have to hold a little bit of back pressure on the elevator stick to keep the nose up to level.
Eventually, you will find a power setting where the nose is pointed straight ahead, you are holding a bit of back pressure, and the plane is descending at something that looks like a comfortable landing descent. This will be your basic approach configuration. Also note that you should not try to manuver (turn) at this speed unless you are comfortable with slow flight or high enough to recover from any mistakes. Also, it's helpful to know that the rudder is definitely your friend when turning or maintaining course in slow flight.
Practice climbing and descending a few times until you are comfortable with the approach configuration above. The next thing to try is to *very gently* ease the elevator back from that position. The goal is to bring the nose up just a little bit without climbing at all (in fact, if you do it right, you should continue to gradually descend even with the nose high).
At this point, you are using the elevator stick as a brake, and the throttle to control your descent. Try feeding in *very gently* a little bit of power while being careful to maintain a constant pitch. As you add power, you should see the rate of descent lessen. Add a bit more power and you should start to gently climb. Reduce the power again, and you can start to descend. Go to idle, and you should descend a bit quicker. If you cannot get a good rate of descent with the nose up and at idle, then your idle is probably too high (or maybe you've got too much pitch on the prop - not likely on a trainer).
Ultimately, after you've practiced these descents at a comfortable altitude, it'll be time to shoot some real approaches. One exercise that I find helps to improve my students' (and my) landings is that I get set up on the approach and cross the runway threshhold in a landing configuration with the nose up. Then, instead of landing, I modulate the throttle as the plane flies down the runway. As you gently add and reduce and add power (while constantly using the elevator stick to maintain the nose-up attitude), you should see the plane climb then descend and then climb again. After you get the hang of this, you should be able to set the plane down on the runway *exactly* where you want it.
I fly at a grass field with lots and lots of overrun space. Because of this, I don't worry about a dead stick during any of these things. If the engine quits, I just land short in the deep grass, or long in the deep grass. Depending on how your field is set up, you should be aware of issues landing short or long. If there are obstacles off the end of the field, don't do the throttle modulation exercise far enough down the runway to have a problem in the event of a dead stick. Also, once you're getting comfortable with all of this, it's a good idea to get into the habit of shooting your entire approach, from downwind to touch down at a low idle. That way, if the engine quits on approach, you'll never land short.
I hope that something here is helpful,
-Wade