Petition before hand as a request for the cerimony. A GM will come and say it.. and help you pick out a place for it to be held. I've had two. One was held in the flying saucer in Qeynos and the other was held on the stairs from the Twlight Sea up to Katta.
The married toons must be 20+, if you wish to have the same surname at the cerimony, which just, makes it more worthwhile, to me. If one or both is under, you can always set it to the agreed-upon surname upon the toon(s) hitting 20, like normal.
GMs tend to bring stocks of No Rent cake and booze to the party. Personally, I'd recommend finding a good baker and brewer to bring their stocks to the party, something appropriate for the occasion.
Make sure everyone isn't drunk berfore hand, though! Then everyone's jabbering on, completely misunderstood, even before the cerimony begins.. and that's no good. :P
Be sure to do the normal stuff, like picking a best man and bride's maid, though they're not nessicary.
Finally, make sure you really want to get married. None of my marriages were really serious.. even at the time of the wedding, I couldn't remember the brides' real life first names (not that I'm good with names to begin with). But, still, you want to check for the basics- like the bride/groom are of the appropriate gender, they're not just trying to leach off of your funds (and the other way around!), and they're not going to embarrase you.
A wedding is, easily, the most social event I've been to in EQ. Make sure you have free time and are in the mood to enjoy it, and give the same consideration for your friends!