Don't take people for granted. Each of us has something unique to offer so get to know others. Show your interest in what others have to say. Find out their needs and how you can help.
By paying attention, you will show that you care and have a genuine interest in the other person. Give good listener cues by keeping good eye contact, smiling, asking insightful questions.
While building up existing relationships, show that you have value to offer by sharing relevant information, events, and others items of note. Ask people to meet you for coffee, lunch, or drinks. Show that you value the relationship.
Over time, you will benefit by builidng strong bonds with your network. When you need help, you won't have to go far for assistance. By honoring your relationships, you will have built up a great network of people, which is a valuable asset.