I haven't had a lot of formal training in painting with acrylics. It's something I've done through trial and error, but mostly something I've done intuitively.
I started this painting, and I was planning on doing the same sort of farm silhouette I've been painting lately, except I'd use the fox-tails as the focus. Once I got going, the fox-tails felt so bland. They couldn't just be black. I took some brown and made more in the background. I took some black and brown and made a foreground. I took some orange and made some highlights. All this was done, and then I stood back and wondered how I knew to do that.
Well, I'm on to other ideas next. I have two window frames that have two, small window panes in each, so I'm going to go back to farm silhouettes again. I'm sure I'll know what to do.