Clone tool question from an After Effects Newbie

I just started using After Effects 6.5 and I have some footage I'd like to clean using the clone tool. I am trying to eliminate a large scratch/scar on a subject who is moving around quite a bit in the shot. What are the proper settings I need to apply in order to do a frame by frame clean? Or are there other nifty effects I can apply to the subject's imperfections? Tutorials available? Please help.

Thank you.
 
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