here are some tips,first the eyes are the spirit of the soul so many emotion are expressed by there,the body is also importante too, if its a chibi figure make it 2 heads long and chibi are always simple to make,if a medium body (cartoony type) you can make it 4-5 heads long,and for more realistic make it 6-7heads long, ok there are tutorials in this page that explain what i said about the bodys here is a link http://www.drawingnow.com/learn-to-draw-meiling.html
also when drawing it is recommended to save your doodles because even doodle can give you great ideas thats what a profesional how to draw manga book i bought said,also i recommend to draw your idea on a seperate piece of paper thats what masashi kishimoto advice on one of his books and dont get frustrated if at first you stink youll improve with practice,practice makes perfect or close to perfect so train alot and in a couple of months youll start to get the hang of it. for more tips just comment me.