But...but...aaah, okay.
First off, harmonized colors are important sometimes.
If you want people to feel well, then you should use colours that fit together pretty much.
Second, express the emotions the image should spread with people, anime girls, animals, objects and other things, like weather and effects.
Finally, take a look at the complete image in general.
Do the colours and people/animals fit your expression/the emotions you want to express?
If not then you might edit some colours, faces, objects and influences.
That`s...the basic? ^_^''