I always find it a bit ironic that the advice given to someone looking for a job is to network. The time to network is when you don't need something. This becomes obvious when you look at the steps to building a successful network:

1) Truly like and enjoy talking and listening to people.

2) Call someone and invite them to lunch, dinner, drinks or just have a conversation over the phone.

3) Ask them about their business, their family, their life.

4) Listen

5) Identify opportunities where someone you know can help this person with one of their issues or problems. Ask permission to connect the two.

6) Call, email or otherwise introduce the person who can help to the person who needs help.

7) Expect nothing in return.

Think about what you've just done. You've helped two people. Do you think they will be more likely to take your calls in the future? 

Expect nothing back, because often, that's what you'll get. That's OK. You'll get something out of it anyway.

Do this enough and you'll have built a powerful network.