Hello, My husband has expereance in dubbing, 
First make sure your surgical scissors,( could be reg scicciers) Are very sharp, and cleaned with alcohol.
Have string ready in case u need to stitch some aeras.
Ok, First, put the birds legs in ice water for a few minutes, this helps with less bleeding from the comb.
When you cut the comb go from face back to the end,
When you are done keep them in cool area becouse if they get to hot it will bleed more.
  The act of dubbing can get an animal injured if not done by a person who is experienced. Roosters will not bleed a lot, or sometimes not bleed at all, if the dubbing is done properly and the nerve is not cut. To avoid perfuse bleeding, you should choose a cool day for dubbing and use really sharp scissors. 
you should cover the rooster completely in a damp towel and take your time to cut and decide how much to cut the comb. There is a natural line that runs along the comb of a rooster. It is always a better idea if you cut just above that line to give it a natural look. We dunk the roosters head in to cold water, We hold there feet in ice water for a few minutes.
Hope this helps u, If u have any ?, u can pm me. 
		
		
	
	
Here is a couple pics my husband did.