Fortunately, when God designed aluminum airplanes (or was it random mutation?) he decided to build some squeezer practice right into the process, in the form of dimpling.
The nice thing about dimpling is that it's so darn easy. If your squeezing is a little crooked, why, the dies will take that rib out of your loose grasp and straighten it right out for you.
But that'd be wasting the experience. Why not put that dimpling to good use, honing your rivet squeezing skills? Try to hold the squeezer square to the part, so that when the dies come together, they're already in perfect alignment. Bring the dies together slowly, see how they look, and get immediate feedback from the part as to whether dimples - and hence rivets - agree with your perception of straight.
And consider this: You're going to be squeezing at all kinds of weird angles, so dimple that way, too. However long it takes to learn to avoid clubbed shop heads, you can cut it in half by "practicing" on dimples.
Hey, lookit that. I'm already talking like I know what I'm doing! Must be time to make another big mistake.
