First of all, is your cast ironed seasoned properly? Check out my Instructable on how to season your cast iron and why I prefer Flax oil. Done? Good, let's go.
Now, let's clean it.
Cleaning cast iron is not difficult. So many people over complicate the matter, or worse yet, do detrimental things to their iron without knowing. You essentially just need two things.
The video is better than the guide below, trust me. There is an entire section of "do not do"