Plan the final composition of your color-field painting, whether as a thumbnail or a sketch on your canvas (top photo). That way, when you start painting, so you can focus on creating the rich color only.
Don't use a ruler or T-square to get straight edges to any area of color. The uneven, softer edge created by painting it by eye produces a far more pleasing result. It feels more natural and contributes to a sense of depth.
Compare the various edges in the middle and lower photos. The orange edge in the middle photo has some of the blue underpainting showing, and the right-hand red edge in the lower photo has some of the orange showing through. There's a resonance or tingling of movement. By comparison, the yellow/red edge in the lower photo is far more precise, far more clinical, flat and boring.
