Create an awesome "About" tab - Make it useful, compelling and memorable for visitors.
Use an attractive main image. It goes without saying that your main image on your Google plus business page is what will create the first impression for visitors.
Turn your avatar into a gallery - One thing that's great about Google plus pages is that you can upload multiple photos for the main avatar. This creates sort of a photo flip-book.
Seek to help your clients/customers instead of only promoting your organization.
Search for conversations around your cause - Comment on those conversations as appropriate. Support other people's agenda before your own.
Hangout - One of the best Google Plus features is Hangouts where organizations can connect with fans, volunteers and donors in a video conference. Hangouts allow for up to 10 people at a time to collaborate on shared documents or just have a casual chat.
Do stuff with others - it can get complicated, especially because Google has a habit of tossing new features out to users to see how they'll respond.