Learning to Draw different Angles

Most of my work so far has been portrait view, so a direct frontal view of the characters, I've always found it hard to draw the eyes at different angles and then the nose and mouth. So have been looking at alot of different pieces for some general idea how artists decide where everything should be, which can be confusing since there are so many different types of characters, but I think generally everyone uses the same measurements.

I have recently submitted 2 pieces at a 45 degree angle, with the subjects looking away, I think next I will try a 90 degree or side view. So drawing smaller eyes and more focus on the hair and its design.