One of the best ways to build a strong professional network is through the presentation of yourself within the field. The more people that know you are active within the field, the more they see or hear your name, the more your network will grow. With some of the new technology for social networking you can present your ideas and information for others to see.
Attending conventions and conferences that are presented by organizations within your field is another good way to build your professional network and learn some of the different tactics others handle some of the issues that you may encounter. These are excellent learning opportunities as well.