There have been public statements from Google’s engineer Matt Cuts that they do not use the +1 as a ranking factor. However, a study by Moz.com shows that there is a great correlation between +1s and rankings. The +1 may not be a ranking factor but it has several SEO benefits. By increasing your Google+ engagement, you reap SEO benefits to your site.
Publicly Recommend on Google
When someone +1s your site, their is a chance that your site will show up to them and their circles higher in Google search results if they are logged in. So how does this help SEO? When most people are researching a subject, they are using Google to find information about that topic. If they have given your site a +1 and it is showing higher because of personalized results, there is a better chance that they may link to it while writing their article. How many times do we write a blog post and keep Google open on a tab for research purposes. This means that if your article is a good source, people are more likely to link to it while they are writing an article. People are more likely to see your post and visit your site if they are logged in. So you can potentially get more visitors and links to your site that way.
How can you build a strategy around this?
If you have a highly engaging Google+ network, you can utilize it to get more +1s. Having a ton of followers is not the most important thing. If you have a million followers who are not engaging with your content on Google+, it will not help you. If someone +1s your Google plus post that contains a link to your page, that page receives a plus also. So you can receive a +1 from your site or your Google Plus post. If a person on Google Plus has the plus one tab enabled, you also receive a dofollow link back to your site (you can only get this type if they +1 from your actual webpage).
Use Pictures on Your Google Plus post!
People are more likely to plus a picture that is embedded than they would a link that is embedded. If you upload a picture and put a link in the description, all +1s to that picture is given to the link and the page it links to. You can improve your chances of getting +1s by building your Google plus network around people with a similar interest.
Google plus in not only about social signals. You can meet many people on Google+ who may link to your content and you may gain knowledge from their content as well. If you like using shortened urls, the plus one passes through the shortened url from Google+ to your site. However, I changed my domain name yesterday and lost all +1s to my site even though it uses a 301 redirect 🙁