It's always a great idea to visit the room where you will be presenting before the event. Sometimes not possible, but worth a few minutes to familiarise yourself with the venue. There may be visual obstructions, such as pillars, which would require you to speak from off centre, or noisy air con units, a busy bar next door. These are all factors that can be dealt with prior to the event, and will make speaking a much less stressful process.
A really important point is: NEVER TRUST TECH!
Venues will tell you how they are well equipped with projectors, microphones, P.A. systems etc., but often when you check them out, they either don't work, or are so old as not to be useful. If you are planning delivering a lot of presentations, then at the very least purchase a good quality radio mic system if you plan to deliver to audiences of more than 50.