In my book, the number-one rule to increase your social reach is be active in social media. You need to do more than just post to your social accounts; you must reach out to other people. You also need to let 
people know you are active in social media. You can achieve this by displaying social icons on your website, blog and e-mail. Of course, creating stuff worth sharing is also very helpful, especially on your blog.
Here is a good post to help you amplify your social reach from Hubspot.