I spread the conditioner on a section of my scalp. Then I use my fingerpads to scrubs at the scalp. But after learning to conditioner wash, this is how I use my ocassional sulfate free shampoo. I think the most important thing is to be thorough. Oh and don't use your fingernails.
I actually made a video on my co-washing method:
Curly Care: Conditioner Washing Curly Hair (Pt 1) - YouTube