The constructs around interaction need to be the same in the online world as the offline. Many people fail to remember this and as such squander opportunity online.

For me, the best results come from 3 key words:

1. Authenticity
   If you are not being true to yourself, respecting others and representing yourself in the same way you would in a face to face scenario, you are not treating people how they like to be treated. Imagine talking to someone F2F and half way through the conversation, they turn and walk away, or change the topic. You would be put off and be jaded by the experience. The same goes online. Do not cut people off, ignore them or talk over them.
   Be authentic online, speak to your strengths, look into things where you need more information and treat people like you would F2F.
2. Content
   Offer unique and interesting content. Everyone can share information, but how you present it (in an authentic way) is pivotal. People love to feel they have taken something out of the exchange. Give them content (video is huge right now) which resonates, adds value and which they will recall. Chances are this will benefit you in the short term.
3. Context
   Make sure the content you are sharing is contextual. Make sure you have considered what you are sharing, thought about why this is relevant to share at the point in time you are sharing it and that it is being shared on the right platform (EG, Depending on your brand, you are better off using Facebook to share more quirky updates than you are on Linked In, where updates tend to be more factual and value adding).
   
   Oh and lastly, Don't jam sales messages down people's throat at every opportunity

I'd say first you have to be providing some value (tangible or intangible). If there isn't value any engagement or loyalty will only be temporary.

• Ensure you are communicating and not just broadcasting (interact with people, it is after all called Social Media, not automated media).
• Ask questions or post polls (just sending out content updates is not enough, ask for feedback and participation and show that you genuinely appreciate it and will use it).
• Try a small giveaway that is based on using a branded hashtag (get customers involved, have them post or submit content and give a genuine award to the best or several best posts).
• Follow up on feedback even if it was bad feedback (use tact, don't ignore or attack customers that post negative reviews, try to solve their issue and do your best to make it right).
• Think about adding a referral bonus or program (give the users a percentage discount or a credit for the additional customers they bring to you).

These are the first ideas that come to mind.