From Seth Godin's book Purple Cow: Transform Your Business by Being Remarkable:

Make a list of competitors who are not trying to be everything to everyone. Are they outperforming you? If you could pick one underserved niche to target (and to dominate), what would it be? Why not launch a product to compete with your own -- a product that does nothing to appeal to this market?

My legal niche to target is going to be woman-owned small business start-ups. What's yours?