Sieglinde de Francesca doesn't recommend explicit lessons for the younger grades (1/2) and just suggests that you model an actual drawing and let the kids learn from your example. But if your children are coming to Waldorf older and you want to let them go "backwards" and have those early experiences, you can do specific lessons on techniques. I'm finding that the kids really benefit from it and are enjoying the material must more, instead of seeing it as babyish. I really recommend her book and DVD. The DVD is especially helpful if you like to see things done instead of just reading about it and trying to copy. The results that you can get from layering the colors are amazing and her DVD has some stunning examples!
Sieglinde suggests if you have a classroom setting to set up three baskets, one for each color. I thought this was genius! Even though you still have to clean your crayons (a cotton cloth napkin and a few drops of Sweet Orange oil works great), you don't have to do it as much as when they're stored in a tin. The yellow especially can pick up colors from its neighbors. Go to A Small Green Footprint to get a set of the three primary colors for $3.55. If you're a classroom teacher, get as many sets as you need! This is cheaper and much more helpful than getting the big Stockmar tins. You can also get the crayons one at a time for $1.50 each if you only need one color. So handy.
The three primary colors in Stockmar terms are:
carmine red, lemon yellow, ultramarine