Use reference images, follow tutorials, even follow non-head organic tutorials, they can be very helpful, here are some I have made that might be useful (One is unfinished due to computer errors):
This one is pretty basic for modelling, but is pretty much the essentials, I hope these can be quite useful, shows some good organic techniques that help me all of the time.
http://seppuku-arts.koetsuaboshi.net/?q=node/5
This one is my tutorial base at Ozark Games, some articles may be of interest, particularly my unfinished head modelling tutorial and my low poly hair tutorial (Without texturing)
http://www.ozarkgames.com/smf/index.php?topic=655.0
And here is one excellent video tutorial, its done in lightwave, but it applicable in most other applications, it doesn't tell you what to do, it just shows you the process of modelling at tutorial, if you use this one, you may want to use my first link of tutorials as a reference, might be handy.
This is one of Kurv Studio's free videos, but you still have to login/sign up to actually view the page. As there are two halves to the video.
There are two head modelling videos together, those are the ones you want to view.
http://www.kurvstudios.com/free_tutorials/lightwave_free_tutorials.php?s=e9ea17c77e52fecf05246d515173d6a8&u=20435
Did The Buddha have a Zen micro?