Good drills for rudder.

Learn to do a stall turn.
Pull straight up, fly vertically STRAIGHT UP. Use the rudder to correct your line. At the top slow the plane, bump the throttle as you full rudder the plane back over to a vertical dive. When you can go straight up, stall over in < 1 wing span you are doing pretty good.

Learn to fly STRAIGHT across the field.
Line up about 50' high 50 yards out and 150yards upwind of yourself and fly STRAIGHT across the field. Use the elevator to correct altitude and the rudder to maintain a straight line down the field. Only use the bare minimum of ailerons just to keep the wings level. DO NOT use the ailerons to bank and correct heading.

Learn to do a really REALLY round loop.
Learn to do a 100' diameter loop. Start and exit at about 100'. Make it as big as your engine has the power to pull it through. Learn to correct with the rudder as the plane is looping to keep it on a heading parallel to the runway through the entire loop. The trick is as the plane enters inverted flight, imagine that your left thumb is on the wingtip that is closest to you. Simply push the rudder stick in the direction that you want that closest (inboard) wingtip to go to maintain heading. Again only use the ailerons to keep the wings level. Try to fly the loop at a constant distance out.. Dont let it wander in or out as you are flying through the loop.

Slightly advanced beginner
Slow roll.
Learn to fly a slow roll. Start to roll and hold the aileron. As the plane rolls towards knife edge start to put in the opposite rudder of the aileron you are inputting. As the plane passes through inverted, come out of the rudder and begin adding down elevator to hold the plane inverted and level. COntinue to roll and as you begin to re enter knife edge start to input the same rudder as the aileron input you are using. As the plane begins to come to upright, ease out of the rudder and level out. Start out trying to do about a 3 second slow roll and as you get better make them longer and longer. Dont let anyone tell you that you cant slow roll a trainer. You might have to increase the rudder to maximum deflection but it most certainly can be done.

That will get you started.