Like a good automobile or a good marriage, your network deserves constant attention. After you find your new position, your natural inclination is to put contact list aside until the next time you might need it.
However, in this new world in which we live, you might need your network very soon, and have to resort to it over and over again during your career. You will almost certainly need your network again; hence you must do what is necessary to keep it active and infuse it with new blood.
Once you accept a job, advise your contacts of your good fortune and new status, and thank them for their help. Tell them that they can rely on you for any assistance they might require down the line.
Never overlook an opportunity to build upon your existing network. Keep going out there in the public realm. Meet new people. Continuously analyze your professional, social, and other contacts for their networking potential.