I learned about this tool from some Discipleship material produced by Perimeter Church in Atlanta, Georgia. The thinking behind it is that the Gospel is just as important for our Sanctification, as it is for our Justification.
The full graphic is shown here. If you click it, you can save the full size version and print it out.
A simpler version is shown here:
The idea is that you write in the middle the Context (i.e. the sin you are struggling with) and then answer the questions and pray through the 3 steps in order: Repent, Believe & Obey.