Once you've layed out your UV's you can export them as an image file (showing all the lines) and load it up in photoshop (or a similar program).

Then its a case of copying and pasting the face onto your image, moving things about and painting areas a bit better.
You can then apply a shader to the head in maya and specify the image file that you are using as the color map. It'll load in and you can see how its going.

Keep making changes in your paint program and refreshing it in maya till you're happy

The main thing that'll determine how easy the face photo will sit on the face is how the UV's have been laid out. Just keep practicing and eventually you'll find a good way to do it.