The stall turn, or hammerhead stall, as many full scale aerobatic pilots call it, is one of the basic aerobatic maneuvers. It is also a pretty and easy maneuver. It's easy because it is done "by the numbers," that is, you move one control, then another control, then another without any overlap. Let's go into more detail.
First, to set up for the maneuver, line up parallel to the runway at full power and at a safe altitude. The maneuver is usually done into the wind and is started after the plane has passed in front of you. You do the stall turn off to one side; you can see the top of the plane as it goes through the maneuver. It is normally used as a turn around at the end of a pass in front of yourself.
After setting up, when the plane is past you and nearly to where you usually turn around, start a pull up about like you were starting a loop. Don't jerk in the up, ease the plane up until it is verticle, then release all the up elevator. Try to keep the wings level during the pull up. Right here, with the plane verticle, do the following: 1. Cut power to idle; 2. Put in full rudder for the turn; 3. After the turn, release the rudder; 4. Ease in power and up elevator to recover to level flight from the dive.
This procedure will work fine if you are flying a pattern plane but it may not if you have a trainer or sport plane. Many planes, however, even though they have ailerons, will roll when rudder is applied. If your plane does this, if it rolls one direction or the other as it rotates through the stall turn, you will have to use aileron to compensate as you do the maneuver. For your first few attempts, do it the way I described and notice what happens. While you are holding the rudder, concentrate on the wings and vary the ailerons as necessary to compensate for the roll. Most high wing planes look like it is trying to do a split-S or to roll over on its back while is is ruddering around. If this is the case, you will have to hold in some opposite aileron during the turn. For example, if you put in right rudder for the stall turn, you'll have to use left aileron to compensate. Low wing planes without enough dihedral will need aileron in the same direction as the rudder. You'll have to decide on which to use by watching your plane.
Another thing your plane might do wrong is not turn at all, but just flop over. Two things can cause a flop. First, if your pull up was not straight, but off to one side, and then you used rudder in the direction opposite to your angle off, the plane will probably flop. Let's say you started the pull up with a little bit of bank and the plane, instead of being exactly verticle, is angling slightly off to the right. Now if you use left rudder for the stall turn, you'll more than likely flop. Watch the plane as you pull up and if it is angling off, use rudder in that direction. This will usually get you a stall turn. Not a pretty one, but a stall turn. You may also run into a plane that likes to stall turn in one direction, but not in the other. If you have one like this, make sure you don't angle off to the bad side during the pull up.
The second thing that can cause a flop over, especially in trainers or slow planes, is not enough speed when you put in the rudder. A pattern plane still has enough speed after the pilot reduces the power to have rudder effectiveness. Speed and a barn door rudder will get you a stall turn every time. On the other hand, if you fly a plane with a lot of drag, like a scale plane or a "stick" type plane that stops dead every time you cut the power, you have to cheat a little. Feed the rudder in simultaneously with the reduction of power. On really slow planes, you may have to put the rudder in first, or only reduce to half power. Experiment to see what works best for your plane. Some planes, even pattern planes, like a burst of power to kick the tail around. For this, you climb, cut power, put in rudder, then give the engine a quick burst of full power and go right back to idle, remembering to keep the rudder in. The prop blast will hit the rudder and start the tail around. Gravity will do the rest.
To recover from a stall turn, release the rudder and let the plane descend. Add power smoothly and blend in elevator for a smooth pull out. Try to make the next exit altitude the same as the entry was.