Once you have chosen a decorator or designer be available to them. If you are able to give your opinions and preferences in a timely manner there is less possibility of mistakes or misunderstandings, and ultimately the project will be completed quicker.
Before starting the project be sure you clearly understand the payment schedule and who is paying for which items. Often the designer or decorator will request that the client purchase items, but others will simply include the purchases in the final bill. Usually designers will ask for some of the cost before starting the project and the balance upon completion.