I would start by making a list of items you want to store. Then think about how much space you need for those items. What will be the best way to store them where they are readily available?
Next would be lighting. What kind of work are you doing, and how should it be lit? I found some track lighting at Home Depot, and there's an adapter you can buy that allows you to simply plug in the lighting to an outlet. It even has its own switch at the outlet. This type doesn't require hard wiring, just an outlet.
Where do you want to work in the space?
I would measure the space and create a floor plan where you can sketch some ideas on how to layout a space. Ask a friend to help you hold the other end of a tape measure, and walk around taking the dimensions. You can then lay it out on quadrille paper, or use free drawing software like Google Sketchup to draw a plan.
The colors of the walls are important to painters, they can reflect into your painting. I don't think its too critical, but if you went with bright yellow or orange, etc. it could make a difference.
Can you give us more info on what type of work you do, then answers could be more specific?
A no trespassing sign on the door