>What is the best way to ensure that you DON'T inadvertently spin the aircraft on turn from base to finals?
Practice simulated base-final turns at altitude until you learn the feel and what the attitude of the plane looks like at various bank angles / speeds etc. Go with an instructor at first if you're unsure.
Flying by "numbers" is all well and good, but you should be able to fly *without* the aid of the AS indicator (VFR of course), just by using the attitude and feel of the plane.
What plane do you fly? Some, like a 172 are very reluctant, almost impossible to spin, even when you *want* them to
Mike