How to grow Facebook groups?

Anyone have experience in growing a Facebook group? Trying to grow one to promote my freelance marketing services and I have a niche group that I know people would be interested in, just don't know how to drive effective traffic.

Try to invite people from similar group or pages

1. Pump up your page first. From there, you can invite your followers to your groups.
2. Expose your page to groups. Post things that the group members could relate to. Some would definitely click the link, some would like your post. Then do number 1.