Mix your neutral colors
The grays and browns that you mix with your palette will ALWAYS be more interesting, and will work better in your painting, than grays and browns you get from the tube. That includes grays that you mix with white and black – a neutral gray that has its uses, but in a painting looks pretty sterile.
Why do the mixed neutral colors work better? They're a little more sophisticated, a little juicier, a little richer and more colorful. They can lean in different directions – you can have cool blue grays, green grays, purpley grays, or beiges, taupes, parchment colors – all created by starting with the same three colors. They give you lots of directions to lean in, which creates a wonderful and subtle variety of ways you can vary the colors in your painting.
And, to continue my family metaphor – they all have the same DNA – the same three colors that mixed to make them. That creates color harmony.