Just one piece of advice from me that I wish my husband had followed:

Listen to your wife and do whatever she says. Even before the birth. When it comes to birthing, she calls the shots, not you. And tell the medical people who are telling her she "needs" to do something she doesn't want where to go: be on her side.

The only other advice would be "become psychic": my DH could have done with that one too, but I don't hold him responsible for that one at least!