Where to begin?
If there is no piece to inspire the space (like the painting in this room or the rug that set the palette here), I like to choose a textile and then determine an overall color palette.
Take a fabric (or rug, bedding, artwork) with multiple colors and pull out your favorites.
Two schemes here, each read in a column. Go for a mix of warm and cool, and throw in a neutral somewhere along the way.
This works with a two-tone fabric, too.
Again with the two schemes. Repeat one of the tones (here, the aqua), ground it (the brown or grey), add a contrast (warm coral or pink to the cool blue), and again with the neutral.
These are process excerpts from a new girls' room project where we are starting with the curtains. It's going to be super cute!