Don't forget to elevate the screens high enough that viewers can see over the heads of those in front. This is one of the most common errors in setting up viewing equipment. If none is available, a light-colored wall may work. While viewing, you must be able to communicate. This means having a telephone to call in questions or get help in case of technical trouble.
Some programs also require access to a fax machine in order to participate.
Find out what is required well before the event. Plan ahead and make sure that it fits the facility and that it's all present. Don't forget phone or fax access, if needed. The most common mistake is waiting until the last minute before testing the downlink and TV or video projector - or not testing them at all. The thing you're most likely to simply forget about is telephone access.