I could have easily made this Career Development Rule #1 considering how strongly I believe in the power of relationships, but in order to properly leverage relationships it takes skills that many don't have, or need to develop.
These relationships comprise what's called social capital, the networks of relationships among people who live and work in a particular society, enabling that society to function effectively.
Networks consist of strong ties and weak ties, and both are important. It's through the building and nurturing of one's networks that career, work, educational, and collaboration opportunities are bred. The key to leveraging the wealth of one's network, by the definition of social capital, is to be a participating contributor to the community in which one belongs by playing a role that one is best suited for, to help it grow. This is called a participation strategy.
We all have something of value to offer our respective communities, and those who belong to it. Providing resources that you have, to build equity within the community, in order to cash in on it later is essential. Whether it be time, money, skills, or knowledge, it engenders goodwill and reciprocity - the very things that will create luck for you in the form of career opportunities down the road.