READ YOUR CONTRACT.
I know this seems so basic but I've seen so many brides fall in love with a site, sign the contract and as the planning process moves ahead they find out they can't have the site ahead of time to decorate OR they can't hang things on the walls OR they have to be out of the site by 10pm when they wanted their wedding to last until midnight. By that time, it is too late to do anything about it, so you end up having to accommodate the site, as opposed to the site accommodating YOU. Read all the details, all the fine print and THEN sign. Some places will even make changes to their contract but they will ONLY do it BEFORE you sign!