1. Before you proceed grab a large sheet and dunk it it in water and then ring out all of the excess water. Hang this sheet on the opening of the fireplace and make sure it it is closed as much as possible on all of the ends. The dampness of the sheet will help in preventing all of the soot from flying all through your house.
2. If your chimney flue is metal, only clean it with a fiberglass brush as a metal brush will wear away the flue in a very short time.