Tips from my wife:
Try it before your wedding; don't do it and go or do it in Vegas because it may take some practice to prevent streaks or other issues.
Exfoliate before you try it.
Bring lots of moisturizer; Vegas is DRY, and you might find that your spray tan flakes.
If you find your spray tan fades, use Mystic Tan Build which comes in both lotion and spray. Here's their website: http://www.mystictan.com/ It will definitely help, and can be useful if you're going direct to honeymoon from Vegas.
My personal advice; don't over-do it, you don't want to look like an Ooompa Loompa on your wedding day or at Vegas clubs, because people will make fun of you.