I used to draw from imagination a lot as a kid, but had no concept

Draw scenes from life first

You won't be able to imagine or paint what you can't understand

>>2648962
thanks

>>2648906
Read through the first couple chapters here so you have an understanding of the theory behind lighting:
http://www.huevaluechroma.com/

Then do studies from life, photos, or masters and try to really analyze and understand WHY each object appears the way it does.

Also don't forget that you can always use reference. Especially for something like a palette, you can use an indirect ref. If you are painting a forest scene from imagination, you can google image some forests and pull them up on the side to see what types of greens typically appear in there, how the leaves might be more yellow when the sunlight passes through them, how the shadows may take on a grey or blue tinge etc.