There are a few guides to consider when drawing the hair. First off, know the direction of the hair. It naturally falls downwards, however, it's possible to create artistic hairstyles which a lot of fashion designers definitely incorporate to their runway collections. Always take note of gravity and other forces that act on the hair. For example, it might be pinned to one side, or you might choose a simple ponytail hairstyle.
The three main guides are:
Point, which is also called the growth point. It makes it easier to draw strands of hair that start from that point. This is useful for drawing the fringe or when hair is secured by a hair tie.
Parting is self explanatory. Different from what I said before, hair doesn't actually grow on one area or point on the head.
Hairline, which is the transition of the hair to the skin. This area of the head should not be a harsh line but a smooth blend, so it's best to use flicking motions.