I've been painting plaids lately. I use them for my craft kits, on the cover and inside. On the back of the instruction sheet there is a nice big piece of plaid paper to upcycle in some way. I love that I never know how the pattern is going to end up looking. There is no pressure to get it right, if there is no right way in the first place. So they've become my version of zentangles. I start with a basic idea of a color palette, but I usually don't stick to it.
First I pencil in a grid. These are centimeter squares. Usually I paint every other square solid, and then fill the spaces in between with diagonal stripes.
Then I fill in the remaining white paper with another color. That's the basic plaid. I like to keep going, because it's a rare opportunity to just be decorative.
Add some blue lines. I try not to be super symmetrical, but it is important that the lines all end up at the same place on the edges of the grid. That way I can put it into a repeat pattern in photoshop later.
Add some green lines.
Lastly I add some light blue squares at the intersections. Plaids often change colors where lines intersect.
It's important to know when to stop. There has to be a little breathing space left.