In 1989, Dr. Steven R. Covey published the landmark book, The Seven Habits of Highly Effective People. If you haven't read it, put it on your Summer reading list right now. In the book, Dr. Covey suggests seven daily activities that we should adopt in our lives to become more effective personally and professionally. One that I reference and paraphrase regularly is Sharpen the Saw (or Axe), which is a call to constantly be reading and learning in order to improve ourselves.
Once you create your profile on Google+ and begin to share updates and interact with other plussers, you will begin to attract followers. Other Google+ users will add you to one or more circles. If you're using Google+ for business, then it's important that you continue to attract more followers so that when you share content regarding your business, more people see it.
When Google enabled the creation and proliferation of Google+ Communities, they did indeed proliferate. In addition to general topic communities, countless other communities sprang up revolving around niche topics and questions, people and businesses, and anything else you might imagine. And since Google continues to make improvements to the communities and moderation tools, community use and growth remains strong.
If you've joined a lot of Google+ communities looking for opportunities for discussion and to meet new people, you're likely a member of at least a few communities that either aren't active, or are not providing you with the valuable discussion you were looking for. These excess communities add to the total number of communities listed on your community page, complicating your ability to find and participate in the communities you're interested in.
One of the interesting features of Google+ is the Explore button. Clicking it reveals "What's hot and recommended" on Google+ (it used to be called "Hot on Google"). These are the posts that are trending, and in fact, to the right of your stream you will see a list of the Google+ hashtags and conversations that are literally trending. You can check out this feed any time you want, and control how many of these items get into your Home stream.