Know what you are going to award in advance, and get it in hand by the start of race time. That way, you're not scrambling to do that last bit of farming or what have you, and you can mail out the prizes or hand them over directly when you announce the winners. I like to give everyone something small for participating, too, as long as I do not expect to have too many players. We have very available stock of WOW gold on most of the servers and we can deliver your WOW gold on the order in a short while. That is the most easy and fast way to buying gold on WOW in the world. 

Have your list of riddles written out ahead of time in whatever form you need to get it to your players. I like to provide my players with three ways of getting their lists, including our guild website, an event channel in game, and lists sent via in-game mail. Any method you use has to be ready to go with the push of a button or two at start time. It helps immensely to have your list prepped and written out somewhere, so that it can just be copied and pasted into whichever form you are using. Don't forget to have the rules, including how players should get the answers to you, written down somewhere for easy copying and pasting; you will have to either write them at the top of all of your lists or repeat them often.

Pick a location for your toon to wait, and be there by the time the event starts. This is helpful because it makes you easy to find over the course of the race, so that your players know where to pick up in-game lists or ask questions. You should be prepared to hand out lists in one form or another throughout the duration of the hunt. In my experience, this hunt does not always handicap latecomers so harshly that they cannot place. Having your toon physically in a set place also means that at the end of the race, you already have a gathering point from which to announce winners and hand out prizes.