First, always finish what you start. Not just in music, but with everything you do. If something was worth starting, then it must be worth finishing. I find that it is best to finish each thing that I start before starting something else, but that is not always possible. Also, give as much care to the end as to the beginning, for it is at the end when things most often fail.
(That was all just a paraphrasing of the Tao Te Ching, by the way.)
I have been working through this book, and I have been enjoying it immensely.
http://www.amazon.com/Composing-Musi...7917244&sr=1-1
Perhaps it will help you, too.