Also play with the attributes found under Turbulence, Spiral and Bend ... they will add a lot of variation to the brush strokes.

Here are some results after playing with the parameters listed above:

All of these are done with a single brush stroke. Spend a few minutes playing with the parameters of the brush and you will end up with some cool brushes for painting the hair. Keep in mind to increase the number of segments located in Tubes->Creation if the strands of hair look like little straight lines connected and also use Path follow located in Tubes->Behavior->Forces if you want the tubes to follow the path of your stroke. Experiment a lot until you find something you are pleased with and then save the canvas as a file type that supports alpha channel and go to Photoshop for further tweaking.

That is all for painting the transparency map using Maya paint effects ... you can paint the diffuse texture at the same time; among those one hundred parameters for the brush settings there are a lot used for the color of the stroke, you can modify the colors, add variations to hue, saturation ... even map textures to the strokes in different modes ... but I will leave that for another time :)

As a final tip: use large canvas sizes for painting in Maya ... if the hair texture is 512 square you may double the resolution in Maya (or go with even for higher resolutions ); you can scale down the texture in Photoshop to the size required ... it is better to have more detail than the lack of detail. After scaling down the image in Photoshop, do not forget to sharpen the transparency map; I use un-sharp mask with the following settings: .4 .5 for the radius and around 100 for the amount ... use the preview option to get a preview of the filter and analyze the result.

The second approach for painting the hair texture is using Photoshop. With some simple custom brushes and a little more time you can achieve even better results than using Maya. The advantage is that you have full control over the strokes and you can shape the hair in whatever form you like ... in Maya paint effects you have a ton of parameters to alter the stroke but it remains a procedural generated stroke.

There are a lot of good tutorials on the internet about painting digital hair (a very good one is here) so I will not insist on this subject more than is necessary.

These are the basic brushes I use:
1. Spackled brush for blocking in the shape
2. Detail brush
3. Single pixel brush for painting individual strands of hair
4. Default Photoshop round brush for rough block in.

Now all you have to do is spend some time drawing some clumps of hair.

Below are a few quick examples.