Instructions:
Stop a moment and take a look at what you've done so far. This is as good a point as any to really consider the curves of the hair because we're about to go into detailing, and it's hell and some more trying to change it much after that. A successful looking hair will have nice, clean, natural lines to it. Even wildly curly hair looks better if the locks flow and work well together, than if it looks like they're just lumped together randomly. Do a separate layer and follow the locks of hair with some brightly painted arrows. Are they all pointing in different directions? If they are, chances are you might want to adjust them unless you're painting hair in motion or some pretty unnatural looking hair.

If it's looking okay, repeat step 6 over the rest of the head.

Common mistakes:
Getting carried away with how fun it is to paint flowing hair. Yes, big bouncy hair is nice, but the eighties are over and gone (hopefully buried) and it's better to keep this in perspective, unless something over-the-top is what you're aiming for. Subtle is often far prettier than overdone.