A clean fireplace and chimney is your best defense against a dangerous chimney fire. See how to clean it in 13 steps at : http://www.ehow.com/how_11052_clean-fireplace-chimney.html
You will need to arm yourself with one or more chimney brushes of the proper size, as well as poles or ropes to work the brushes through the chimney - the equipment you need can be purchased at most fireplace and woodstove equipment stores, home centers, hardware stores and some other retailers.
When doing the work yourself, take your time, be careful and follow some common sense rules. Use a sturdy ladder of the appropriate size for the job, wear appropriate clothing and slip-resistant footwear and never overextend yourself on the roof - it only takes one slip to result in disaster.
http://www.doityourself.com/stry/cleanchimney
Some more sites:
http://www.northlineexpress.com/help_chimney_cleaning.asp
