I was looking at a friend's drawing and was reminded of a point in my learning where I was a bit stalled on getting the realism into my drawings...my problem in hindsight was simply not sitting down and critically analyzing features in perspective. There generally are 3 basic views and of course countless variations with more complicated posing but to start out these are the basics.

Once that is nailed it isn't difficult to remember to look for the variance. It might be subtle but it's important to foreshorten the features as you note the changes if the head begins to turn away at all.