You work with people. Those people know people. They know other people. Someone says 'I need a good PHP guy' and a guy in the network replies 'I know a guy, SadWebDeveloper - here is his email address'. Boom: you have made contact with someone who wants to hire you.
Join the Whatever User Group in your area. Go to the meetings - introduce yourself. Be a presence on their mail list. Boom: more networking contacts.
This is a really good example. TJIC and I have talked on the internet for -years- via email and twitter and blog. A customer of mine mentioned she was looking for a local developer (Los Angeles) but couldn't find anyone who met even her minimal standards.
I said 'Hey, I know a guy', he lives 8,000 miles away, he's about a hermit and a half, and he knows his sh*t' and a few weeks later TJIC got some months of work and everyone was happy.
And now, here we are, talking. Maybe I can be converted to a networking contact. You never know, hunh?