The key to a successful Facebook Group is to gather like-minded people with shared interests and spark conversations between them. With that in mind, create a Facebook Group that's either about your blog's topic or a related topic where you can weave in your blog on ocassion.
Step 1: Log into your Facebook account and select the "Groups" link on the far left side of the page.
Step 2: Select the "Create a New Group" tab from the top menu bar.
Step 3: A form opens with some required and many optional fields for you to fill out with all the necessary information to start your group. For example, name your group, describe it, determine whether its a public or private group (make it public if you're using it to promote your blog), upload a picture, and so on. The more information you take the time to provide, the better.
Step 4: Invite your Facebook friends to join your group, and promote your group on your Facebook profile, in your blog, in your Twitter account, etc. to get the word out. Then start posting questions to the group, useful information, links to your blog (without overdoing it), and more to make the group lively, helpful, and enjoyable. The more active your group is, the more popular it is likely to become.