I'll be the first to admin that I am terrible at this, I've been a best man, and I've been a groomsman many times, and my entrances were nothing special.
You will likely be paired up with one of the bridesmaids. If you have some rhythm, you can bust out your best dance moves with her and that is enough.
If dancing isn't your thing (I dread it) you can come up with a little skit or routine to act out... but again I'm not too much help there. There are some examples (many of them suck) on youtube if you search around.