1. You tell a sweet, sappy story about how when the bride and groom got together, you "knew" it would be forever (I think this increases the statistical likelihood of a subsequent divorce)

2. You tell a funny story that gets everyone laughing and indirectly show how the couple is "meant to be together"

OR (my favorite)

3. You embarrass the groom by telling everyone something that they never knew (example: at my friend's wedding, his best man started by saying, "I'm going to tell you about the big motorcycle accident in college - and I'm sure you're thinking to yourselves that the groom never had a motorcycle, or the money to buy one back then, or a license. Well, you're wrong if that's what you're thinking." And it just got better from there)