I've been running networking groups since 1996. The ones that succeed have a good mix of professionals who understand how to look for opportunities for each other. It's even better if those professionals are involved in other networking groups so they can constantly add more value to yours.
People always ask me what sort of professionals should they have in the network. While it's important to have those business types that compliment what you do, it's also good to have a random mix. Here are the Top 20 Professionals You Need in Your Network.