Honestly, you should read one of these tutorials, or at least get some inspirations:
http://www.polykarbon.com/tutorials/malehead/3quarter1.htm
http://www.polykarbon.com/tutorials/frontview/frontview.htm
http://elfwood.lysator.liu.se/farp/face_n_head_1/FandH.html
http://www.anticz.com/heads.htm
The human face isn't easy to draw. Even, or especially, as a Manga artist, you should know some basic anatomic details, so the character doesn't look, well, retarded.
http://www.polykarbon.com/tutorials/malehead/3quarter1.htm
http://www.polykarbon.com/tutorials/frontview/frontview.htm
http://elfwood.lysator.liu.se/farp/face_n_head_1/FandH.html
http://www.anticz.com/heads.htm
The human face isn't easy to draw. Even, or especially, as a Manga artist, you should know some basic anatomic details, so the character doesn't look, well, retarded.