The many bristles of a hair brush might be great for detangling hair, but they can also trap all sorts of filth. The tool to clean a hairbrush? A toothbrush.
Anithamallya's instructions are very simple: After getting all the hair strands out of the bristles (use scissors or tweezers), put the hair brush in a bowl of hot water with a few drops of shampoo or dishwashing liquid. Scrub with the toothbrush, let soak, and then dry.
Do this every now and then to make sure you aren't adding little hair-tangling fuzzies to your hair while you're brushing it.