Drawing curly hair is one of the toughest jobs out there. But at the same time, there is a trick with which you can do it.
First, you need to draw two parallel lines in a slightly slanted manner. Then, trace out a wave which touches both the parallel lines as shown below.
Once you are done with one wave, trace out one more wave and then join their ends. Start giving textures between the parallel lines to make it look like a hair. You can follow the steps shown in the picture above.
LearnDrawing 