First think about colors that make you happiest. Are you more of a bright color person, or do you prefer neutrals, or colors from the same palette? Next, think about the type of work you're doing in your office. Are you seeing patients? If so, you'll probably want to pick something that's calming and not distracting for your patients.
(Elle Decor)Depending on your office (and how forgiving your company is), my next inclination is always to paint. In a small space, keep the paint colors light to make the space seem as big as possible, but try using a high gloss paint. The reflective quality of the paint will make even the darkest spaces seem lighter.
(House Beautiful)Another trick, why not add visual interest to the room by painting the ceiling a different color? (One note: If you're lacking height, try to keep the ceiling color on the lighter side to keep the room from feeling like it's caving in on you.)
Blik and on Etsy.
Once you've painted, or added decals to your wall, next stop is accessories. If your office furniture comes with the space, try adding some color and texture to the room with pillows, or a great mirror.
(Williams-Sonoma Home)If you have a bookcase full of books or manuals, try arranging them by color or size to add some interest to your bookshelf. Add a few personal touches (i.e. pictures, a cool vase, etc) too.
More small office ideas coming tomorrow...