Everyone knows it’s important to build a network. But once you’ve made a connection with someone, how do you maintain it over the long haul so that you can call the person when you need a job reference or a professional favor? The first step is to determine whom you want to stay in touch with based on their professional value and relevance to your career. Look for current and potential clients, influential colleagues, and friends who are superb connectors. Then figure out how often to be in touch. Some experts suggest having 10 people you’re in regular contact with, 50 you reach out to every quarter, and another 100 you’re in touch with once per year. When you do reach out, find ways to show that you’re interested in their lives. Ask how you can be helpful to them. Every six months or so, regroup and make sure you’re in touch with the right people. It’s natural for your list of professional ties to change as your career progresses.