Whenever I can, I paint the powerful and obvious things in my subject first.
Use lots of paint and don't worry, they will make more.
Never knowingly leave anything wrong on your canvas.
Be flexible - the order in which you introduce the elements of a painting should not be a rigid system. What worked last time may not work this time.
You can stick with a few clear-cut values, which are stronger than a multitude of values and will obviously yield a stronger painting. But not all subjects or light conditions appear that way... be sensible and paint with values that are appropriate and faithful to your subject.
Paint like a pig eats.
Scan your subject for things that are clearly impossible. After all, paint isn't magic! If you see that certain elements in the subject are beyond the limits of your pigments, try to form an idea beforehand of how you are going to handle those areas when you get to them.
