Most people will say to add a little white to the paint but don't do it since it it causes paint to have more of a pastel tone. Go to your paint store and ask for a Color Wheel. Look at your color on it and it will give a corresponding shade to add to tone it down.
If you aren't willing to change the paint color then you can go out and purchase darker accessories for your room. Dark curtains, wall art and furniture help take some of the focus away from your slightly too bright wall color.