Here is what Katherine van Schoonhoven gleaned from seeing his video:
1. Look for a good white shape in your design. It should be about 1/3 of the paper and touch 3 sides. It should be irregular, unpredictable, and oblique.
2. Establish dominance. Shape dominance -- geometric or curvilinear temperature dominance -- warm or cool. The 80/20 rule works well in establishing approximately how much of which. Dominance gives cohesion to a painting. Avoid 50/50 because it violates the idea of dominance.
3. Ideas for keeping painting interesting:
add texture -- use techniques without drawing undue attention to them ..salt, stamping, lifting, atomizer, ...(Salminen's work is watercolor..and I skipped this as salt and oil paint doesn't seem compatible. haha)
edges -- pay attention to the edges and use them to create intensity
linkage -- stepping values between dark shape and white/light shape
repetition -- design element that adds unity.
center of interest -- this area should have the strongest value contrast.