There is great value in painting your own value scale. You can do one in pencil, acrylics or oil. Value is probably more important than color in giving a painting depth and creating form. It takes at least three values to give an object shape.
Something that helped me as I struggled with this was to pre-mix my colors into at least three values before I even started to paint. The three value of green give you an idea of what I mean.
I still keep a value scale next to my easel as a reminder. Once colors fall into the same value, the painting starts to look flat.