JM: My plane won't go straight up!
GA: Do you use your rudder?
JM: Yeah, for taxiing, right?
GA: Well, true, but it does have some other uses.
JM: Oh yeah, takeoffs and stall turns.
GA: If you want to do nice looking maneuvers you'll need to use the rudder.

It was at that point that I knew I needed to learn how to use the rudder if I was going to improve. I needed a starting point, some rudder rules, if you please!
Although using the rudder, in most cases, is not intuitive for me yet, I'd like to pass on to you a way to think about using the rudder. It is certainly not the only way, and maybe not even the best way, but you have to start somewhere.

Ideally, your aircraft would have a pure response to the rudder: when you push right rudder the nose moves right (yaws) without rolling. Since I don't have an ideal airplane, or a computer radio with mixing functions, I have to use some aileron to keep the wings level. I also took another piece of advice and stand with my shoulders square to the flight line for the whole flight. I was told this position gives me the best chance to develop a clear mental picture of the needed corrections. The following suggestions may seem mechanical, but with enough practice my hope is they will become intuitive and automatic.

Rule #1. Rolling from upright to inverted, the sticks go in the opposite directions: right roll - left rudder, left roll - right rudder.

Rule #2. Rolling from inverted to upright, the sticks go in the same direction: right roll - right rudder, left roll - left rudder.

Rule #3. When the line of flight needs to be corrected and the plane is upright, push the rudder in the direction the nose of the plane needs to go. If the nose needs to move right, push right rudder.

Rule #4. When the line of flight needs to be corrected and the plane is inverted,
and coming towards you, push the rudder in the direction the nose of the plane needs to go. If the nose needs to move right, push right rudder. Use your eyes as the direction for the rudder. Your head is turned towards the plane so push the rudder towards the eye that would put the nose where you want it. Once the plane is going away from you, push the tail in the direction it needs to move. If the tail needs to move left, push left rudder. Push it toward the required eye. Think about using your left and right eye as rudder guides during inverted flight.

These are four basic rules that really helped me. There are three basic maneuvers that incorporate the four rules: (A) flying back and forth in a straight line, (B) the Half Reverse Cuban Eight, (C) the Loop.

A. Do a complete flight of just flying back and forth keeping the plane in a straight line along a pre-chosen path. Use the rudder coming towards you and going away while visualizing yourself in the cockpit. Start your corrections very gently as soon as you notice the need. Release the correction as quickly as possible. To fly a straight line you may need to correct constantly or hold the correction!

B. Half Reverse Cuban Eight: (from level flight, just as the airplane passes in front of you, pull up into a 45 degree climb, roll to inverted, complete the loop back to level flight going the other way.) Since you are always looking at the tail of the airplane when you start this maneuver just push the rudder in the direction the nose needs to move (Rule #3) and release that correction. Now roll to inverted (Rule #1). Since you are going away from yourself, inverted, push the tail in the direction it needs to go (Rule #4). Now combine the first two maneuvers and burn a couple tanks of gas and using the rudder starts to make sense.

C. Loop: When starting the loop push the nose in the direction it needs to go. As the plane comes inverted, you are looking at an inverted plane coming towards you, and just push the nose in the direction it needs to go (Rule #4 - use your eyes). Finish the loop and make any corrections needed coming down and out.