Networking is an art, of course--engaging others, offering them solutions, finding a great mix of people who may be in a position to return a favor in the eventual future.
But there's a deliberate set of calculations that can help sharpen your network's effectiveness.
First, consider the mix of people; Harvard Business Review suggests a ratio of 2 insiders and one outsider. In other words, cultivate relationships with people who have various perspectives on a given company, field of inquiry, or other parameters of your job search. Read more here: http://blogs.hbr.org/2013/10/to-diversify-your-network-follow/
Second, understand that people you don't know well may be exactly the people who can refer you to a great job--because they don't run in exactly the same circles you and your friends inhabit. The key to getting these folks to help you is "tie activation." Read more here: http://www.glassdoor.com/blog/personal-connections-matter-hired/