Here is a great blog post by Sinclair Ferguson on Mortifying Sin.  It is definitely worth a read.

http://www.ligonier.org/blog/how-mortify-sin/

In this blog, Ferguson walks through Colossians 3 and gives some incredible wisdom on what it means as believers to kill sin.  One thing i particularly found helpful is the fact that we do not “put to death” our sin in isolation from “putting on our new self”.  These actions are not to be separated.  We do not just reject sin but because of the Spirit working in us, we exchange the desire of sin for the desire of holiness.

Check out the post.  It will not disappoint.