Recently, I helped style an event that was held in a gorgeous rented hall. I hadn't been there in ages and was immediately taken by the beauty of the space, and looked forward to gilding the lily.
According to my collegue, our client had a rough idea of what she wanted, and asked us to come up with the final design on the spot, using a selection of raw materials. While I actually enjoyed the design challenge and the finished product looked very nice, we probably could have done an even better job with some advance planning and proper tools (honestly, there were a few times when I wondered if I was on some sort of reality show..."Can Team A pull this event together in just three hours with nothing but fishing line and packing tape?")
The lesson here is this - overcommunicate your vision to anyone who will be helping you AND plan ahead! Take into account the architecture of the space. If you want things hung up, consider ceiling height and if you'll need to do any installations (3M Command hooks are a godsend!). Make sure sturdy ladders are available. If you're doing any sort of draping, remember that you're dealing with gravity, which has an exponential effect when a piece of fabric or other material has to cover a wide distance, such as the example here:
Studio in a School dinner by Van Wyck & Van Wyck, New York. Photo by Mary Hilliard
If at all possible, set up the day before. This will do two things - 1) give your decorators enough time to account for any unforeseen issues and 2) if the decorations are strong enough to withstand the night, you know there's no danger of them drooping during your party. I know getting early access isn't always possible, but if you have that luxury, by all means take advantage of it!