I'm not an expert, but it sounds like you've already got the main points. Perhaps you should remove deadwood as well.

All I know is that I need to cut any crossing branches but what else?
- 'inside the trunk curve' branches
- 'point straight' branches
- 'point straight up' branches
- 'growing on the main trunk' sucker
- 'blocking the trunk' leaf thinning
- 'bar branch' or 'opposing branch' removing, choose the outside curve. (oh you got that covered already)
- remove suckers from the graft.
- 'vertical opposing branch' growth
- any branch more that two nodes long before a branch split.

Currently the branches touch the ground. Is this ok?
- it's ok
- i cut mine back

Also, when is the best time to prune?
-anytime, anyday

also look up maple pinching and the gardenweb maple forum too.