Jack,
i think the best way to break in a glove is to simply just play catch. You can always throw and throw and doing so would break in your glove and also work on your arm strength. I think its best to focus on catching the ball in the pocket and squeezing the glove according to how you want to break it in. An infielders mitt is very different from the outfielders glove. One of my teammates in college would wrap a lacross ball in duct tape and tape it to a thick stick and just pound the pocket of the glove with it. Fortunately they sell those now at Sporting good stores.
I hope this helps
