The next time you're at a wedding, when the bride's coming down the aisle...look at the groom's face.
Typically my favorite part of the wedding. And you can learn a lot from it.
Me? Oh, I was bawling at that moment during mine.
Which leads me to Tip #2 if you're not married yet. Don't take pictures beforehand. That moment is too magical to ruin it by seeing your future spouse ahead of time.