Learn to draw a basic, generic face first using realistic construction methods, then in order capture your friend's likeness, you just need to adjust the placement of the construction lines used to create a realistic head, so that they match the proportions of your friend's face.
exactly.. watch the these videos and search lots of tutorial from youtube, dailymotion or any other online videos. download them and follow them one step at a time.. like how you used to start drawing anime.. you have the passion and determination there.. if there's a will there's a way. good luck bro, I'm still building up long rusty skill as well... hahahaa