An Avistar properly set up as a trainer won't spin well. Its a dual purpose aircraft, introductory trainer and basic aerobatics, so it never will spin like a CAP or a Fun Fly plane. (not if you want to be able to recover from the spin...)

Move the CG back a little (1/8 to 1/4 inch) at a time, (preferably by moving the battery) to no further than 3/4 inch behind where its marked on the instructions. If its too far back, getting OUT of the spin can be impossible.

Changing the aileron center position can also enhance or reduce "spinnability" of a plane. turn the clevices 1/2 turn at a time to lower both ailerons. You have it right when instead of stalling flat, straight forward, it begins to drop a wing (usually the left with power on.)

Its also possible to warp the ailerons to drop at the tips, overcomming the built-in washout of the Avistar wing. Be REALLY careful here... stalls can become very unpredictable. Snapping into a spin on landing approach is rough on airplanes...

Make ONE slight change at a time. You are destabilizing the aircraft... it can get really hard to control after a slight CG change. If it begins to get hard to control as the fuel depletes, land immediately and move the CG forward 1/4 inch.

To test stall characteristics and to practice spin entry and recovery fly WAY UP HIGH! If its hard to get out of the spin, (normal rudder opposite isn't workng) turn ailerons and rudder INTO the spin with full down elevator and full power to convert to a spiral dive. (rudder input is momentary, then centered as soon as the plane changes path/rotation speed) If its had to get out of a spin... go back to the previous CG/aileron configuration. (if inverted spinning... elevator and rudder are reversed.)