Businesses tend to see clients or customers as separate individuals. When it comes to online communities it's better to think of them as an interconnected network. Individuals in the network link and communicate with each other. You want potential customers to link with you.
The first step is to create a Facebook and Twitter account. If your business sells to other businesses or professionals, you could also consider opening a LinkedIn account.
The secret to Facebook and Twitter is to post a steady stream of high quality content, that is relevant to your niche. Whenever I write a new business related article or if I find a great YouTube video or forum discussion, I share it with my subscribers. This establishes credibility, then if you recommend a product or service the chances of it converting into a sale is much higher.
To follow me on Facebook, login to your account, follow the link below, then go to the top-right part of the page and click on 'Subscribe'.
With both of these sites, when you share something all your subscribers or followers see it. It can also go viral if they retweet or reshare, what you showed them, because then everyone they are linked to also have a look at it. That makes Facebook and Twitter incredibly powerful viral advertising tools.