Much of how users actually engage on the network is the same as on Twitter and Facebook. However, because circles force categorization of people, Google+ is far more easily customizable and allows a greater level of flexibility and dialed privacy. This would, in theory, allow users to enjoy the network with more people in more relevant ways. For example, you could share content specific to your professional network with people in that circle, while sharing the pictures of your kids to a more private circle, all from the same platform.
MATLAB: A company that helps coding professionals better use their respective languages, MATLAB continuously provides its community with educational tools. They share content from their six blogs and numerous webinar series, offering an official certification program and general advocacy to grow the coding profession. Additionally, they reach out to audiences speaking both English and Japanese.
Add value: Create good stuff. While trite, it is true. Giving people something to get excited about and a reason to want to follow you is the best way to grow your community. Google+ allows you to target who gets to see your content if you wish, so use that tool to your advantage and get creative. Can you create a special circle just for your top influencers and advocates? You betcha! The sky's the limit!
Engage: If you're putting out quality content and giving people a reason and opportunity to engage with you, you must be there to back-up that conversation. Be there to get involved, address questions, and add to the conversation.