"One Hour Compo" (or OHC) is a weekly composition competition (or "Compo") where participants are given a theme along with one hour to compose an original track based on the theme. I have participated in OHC regularly since OHC077 in early 2010, and the regular weekly practice has played an integral part in shaping my composition workflow and giving me a chance to experiment with and practice my production skills and techniques.
You can visit One Hour Compo at http://compo.thasauce.net/compos/view/OHC.
You can view a listing of my One Hour Compo statistics and placements here.