As an organiser you should know exactly where you are going on the day and what you need. Namebadges (sticky labels and pen if nothing else) will be needed at registration, if you have tickets and need to tick people off then rope in lots of volunteers (it sounds like a lot but 3-5% of your total attendee count is ideal) and brief them, and spread out across as much space as you have so you can parallelise as much as possible - registration is always chaos because of course everyone shows up at once and causes a backlog!If your event has a timetable, this should be posted on the walls and also given as a handout so everyone knows what is happening where. Have room managers to let speakers know when their session is over and to wrestle people off the stage (yes, seriously) if they run over their slot! When you run to time, people get fed when they expect to and don't have to climb out over the rest of the audience when they have to rush off to catch their train or whatever because the event should have finished. It just makes the whole thing less stressful for everyone.
In the morning, make sure you are at the venue well before your attendees to check wifi, projectors, sound, room layout, setup registration and welcome any early arrivals and direct them at the coffee. If you have exhibitors then you'll need to make sure they can get access a couple of hours ahead of the doors opening. The upshot of this is that you will be hosting the conference social at midnight and letting exhibitors into the venue at 7am, possibly for a number of days in a row ... event organising is physically and emotionally demanding and if you are having fun with your friends then you are probably doing it wrong (harsh but the best conference hosts I know keep circulating and hosting from dawn to dusk and beyond).
During the event, keep an eye on twitter and run searches for your hashtag. This is a great way to know that one of the rooms is too hot/cold or that people aren't sure what time something is happening. Use the official account to respond to these enquiries and tag your responses with the hashtag too so everyone sees your message as well as the complaints.
Most of all, remember that if you guests have the impression that the event is going smoothly, then it probably is! As an organiser you see all the small behind-the-scenes crises, but if they are invisible to the average attendee, then you're doing really well :)
Do you have any more on-the-big-day advice for events? Add a comment!