Determining a palette is very important when pulling a room together! I often use nature as a reference, a colourwheel, artwork of course or anything that triggers a reaction when i see it! In short, choose a palette with no more than 4 colours for a room. Walls and trims count as 2, the other 2 are your furnishings and accents!.. I like to work within three nuances on the colourwheel (3 adjacent colours), or complimentary colours (opposites on the colourwheel). They are available in any art supply stores.
Here are a few inspirational images that will hopefully show how to extract whats out there in order to create flawless rooms that you will love forever! Dont forget to ever take a few minutes to look at things... This will train your eyes!
(Images courtesy: La maison Boheme, Kelly Weastler blue tray, painting by Micah Candrall)