My advice for mechanical comprehension is to study a middle school level physics text. You don't need to know physics formulas, just the conceptual stuff - and it's an easy read. I was teaching 8th grade science when I took it, and I did well enough to be a pilot. The only practice you need for spatial apperception is looking at really crummy drawings of a pilot's view. On the real test they were actually worse than in the ARCO book - and those were pretty low quality. The key is not to pretend you are a pilot in that plane, but rather to mark where the horizon is in relation to the picture box. If it's below center, you're pulling up, etc... I know ... duh, but sometimes you'll miss it at first glance because it's only a little below center. The tricky ones are when you are banking and pulling up/down, but if you think of it geometrically, it's foolproof. I got 100% and I'm a fool.