There have been several good suggestions and information and you will need to glean from that what you think is applicable to your experience and skills. I am a CFII and used to fly full scale aerobatics and can give you some suggestions on techniques to use to slow the airplane for landing. As a student pilot I won a few spot landing contests using the same technique. The technique can be used for RC airplanes. I think it would be better for you to just keep it simple for now and you could add or refine the different landing methods later.

Perhaps something that you might be doing is attempting to slow the airplane down while on final which will result in hunting for a way to get it down on the runway, when actually you should be slowing down much earlier.
You should practice flying the pattern at the same altitude and distance from the runway as best you can, which will allow you to start your descent at the same point. Your descent is started by reducing the throttle and adding a little up elevator. Practicing slow flight will help with that. The point which you choose to do this should be somewhere opposite the end of the runway when on the downwind leg or as you turn on base. Flying the pattern at the same altitude and distance from the runway will allow you to start slowing down at approximately the same point.

As you turn on final do not change anything and watch how it is doing. After establishing the descent you will get an idea if you are going to be too high or too low. Note that when you are making the pattern turns you will lose some altitude so, to maintain the same descent you will need to add a little back pressure on the stick or elevator.

If too high reduce the throttle, if not already at idle, and add UP elevator. If you are already at idle then that is where it gets a little more complicated. If you have plenty of runway, which is another advantage of the above technique, then just let it land, or you can choose to go around. The next time you can adjust either the pattern altitude, distance from the runway or the point at which you reduce the throttle. You can later try side slipping and other techniques as you learn them, but keep in mind that you should not have to use those techniques if your approach is done correctly. Side slipping is a way to loose altitude fast and can be used for landing on approach over an obstacle, short fields and high crosswinds.

If you are going to be too low then add a little throttle and nothing else. Watch what it is doing and make adjustments as necessary. Remember throttle controls altitude and elevator controls speed in this configuration. Same thing, next time adjust pattern altitude, distance from the runway, or the point which you reduce the throttle. You are inviting problems if you try using the elevator to gain altitude when the airplane is flying at a slow airspeed, which again is where knowing the stall speed is important.

Remember that you can add throttle if you think it doesn’t look right and go around. Slowing the airplane down begins much earlier than while on final. This is basic landing techniques and there are many more things that I have not even touched on that you can learn later. The best thing to do is to practice and then practice some more. I hope this helps.