Robin Good: Here is a truly comprehensive Google+ SEO guide which covers every aspect of Google+ and how it impacts your visibility inside search results.
Key sections in this guide include:
Google+ Search FacetsGoogle+ Search ResultsGoogle+ People and Pages ResultsGoogle+ Search SpamSearch+People and PagesGoogle+ PostsGoogle +1 ButtonGoogle+ Social SnippetsGoogle+ ContentGoogle+ FormattingGoogle+ Brand PagesGoogle+ AuthorshipGoogle+ InfluenceCircle Count
Three key takeaways:
1) Google+ search results are personalized but through some crowdsourcing I’ve been able to determine the search signals.
The most important signal is whether the query term appears in the Introduction, Employment, Education or Places lived section of your profile. Danny Sullivan rarely shows up in a search for SEO because he doesn’t have the term in any of those fields.
2) People and Pages are defined, curated lists of people by topic. That means there’s nothing you can really do to optimize for these slots.
3) Panda separated low-quality and high-quality sites. AuthorRank would do the same for people and their associated content. As the tidal wave of digital content roars in Google’s ears finding ways to sort the good from the bad quickly will be of increasing importance. Content without Authorship could become a second-class citizen.