Marketing Strategy: How can I narrow down what target market or niche to focus on?

Choose a niche where: 1. You enjoy the work. 2. You already have some satisfied clients. 3. There is an ecosystem of related professions (ex: realtors, bankers, title companies, lawyers, home inspectors). Number three is important because solid businesses are built on a pipeline of referrals, and clients won't give referrals to competitors. So, for example, if you are a web designer focused on real estate agents, don't ask for referrals to other agents. Ask for referrals to real estate lawyers, home inspectors, bankers. The agent would gladly give them to you.  Then, build relationships with them, saying that you design websites for real estate agents. They refer you to agents and you can refer them to agents. Then, when you get new real estate agent clients, ask them for lawyers, inspectors, etc. So it becomes a virtuous cycle. Also, if you are reluctant to pick a niche, remember that a niche is for outgoing marketing only. If people from other niches come to you, then feel free to work with them. So you really aren't limited yourself to the niche.