My best tip, is to try to choose at least 1 decisive vision you have, and then build/move everything around that choice, try to reverse engineer the rest of the color! I usually go into something, knowing something like, "I don't want to use any brown", "I want the grass to be blue"... "I want red to be the most important shade"

Lets say, you want the bark of the trees to stylize orange, not brown... what kind of lighting could justify that, what color would the leaves be, the grass, to make that orange look natural, FEEL like brown? If the bark of the tree is orange, it might not look rational if the sky is simply normal blue, and the grass normal fully lit green (but that could be your point, if you wanted it to be). It's difficult to describe this, as I don't want to impose any absolute rules... (I dislike tutorials that just teach you to copy someone else's color! I'd like you to find your own harmony!)... but, try to pull a kind of logic gradually, out of things, based on what you want the color to do.

Maybe you want your purple character's fur to be black for this piece... we need to then move everything around that. If their fur is black, what other dark colors will become black, too? Maybe anything typically blue, purple, brown, is now black, swallowed in this lighting. What is left to 'pop'? Maybe only orange, yellow, is catching the light....

In this way, building a room or setting, around that central color inspiration, can lead or follow. "I want the bright red wagon this character is sitting in to be visually striking". Alright, that means everything else should accent that red somehow... do we desaturate everything else? Or make everything else more monochromatic? Or darken everything? Or make everything pale? How do we want the red to 'stand out'? Bright, like a light.... shining against dark background? Or do we want it to be leeching color from everything around it, feel like the world is dead?

As always, I think looking at photography helps.... or the world around you. I'm always agog at color. My husband and I's skintones, in the usual overhead lighting, are so different.... and then, under others, like a grey starlight, both so equalized, even though I know we're different. This plasticity is reality.