Dry Erase

This tool will help you out A LOT. When you want to check your spacing, or track your arcs, or explain something to someone else by illustrating it on top of your animation, then drawing on your monitor is the solution, but be carefull, no permanent marker, no Sharpie, use a DRY ERASE marker, like the ones from Expo.

So if you need to track the spacing of a bouncing ball, then choose a point of reference, either the middle of the ball, the top or the bottom, then start drawing a mark on your computer (every frame, every 2nd frame, where ever you need it to be).

If you do a walk cycle and you want to check your figure eight arcs on your arms, then choose the wrist, something "stable". I wouldn't choose a hand or a finger, because that part of the hand is going to move differently than the arm.