Social Media Marketing

my wife and her brother own a jewellery shop in Dublin which is a little out of the way, and advertising budgets are limited... any ideas on how we can promote it using social media techniques? Anyone had any success with this? Many thanks for any suggestions

I really need to know how many ways there are too join a group and how you actually do it. Its important because a friend of mine has a disciplinary at work tomorrow with regards to stuff that has been put on facebook. All help is much appreciated. Many thanks in advance.