Okay, now we're ready to really begin.

1. The first thing I do before drawing hair is to do any touch-ups on other parts of the image that may be needed. This includes fixing elbows, etc. I usually do this directly in the layer with the hair props, as that is the one that will mostly become the final image.
2. Next, I remove unwanted parts of the hair prop. In the example below, if you flip back to page 2 you'll see that the woman has a couple strands of hair dangling in front of her forehead which were part of the hair prop. To erase them, I simply use the eraser tool in the layer with the hair prop. This allows the "bald" layer underneath to show through. Just like magic, the strand is gone. Because the two images match exactly except for the hair, there's no guesswork involved. This is a lot more accurate and foolproof than using even the beloved cloning tool.
3. When I'm done fixing things, I create a new, empty layer on top of the others. It is in this layer that I will do the actual hair drawing. Using a separate layer makes it easy to fix things and tweak the hair without risk to the underlying image.
4. When drawing hair, I usually start with a dark color. I draw one strand at a time. This can be a bit tedious, but it really doesn't take all that long and I like the results. I follow the general contours of the hair prop.