A couple days ago I found an interesting discussion in Flickr. In the wedding photographers group some of the members were discussing about how to get business through social networks. The idea is simple, but effective: Post the pictures you take for a senior portraits session, engagement or a wedding on your Facebook and tag your customers. If your privacy options are set up so everyone can see those pictures, allow comments, and you will be the guy who took those cool senior portraits or those cute engagement shots, and that will surely bring you business.
The same idea applies to many different businesses. If you do a good job in whatever you do, you can probably ask that customer to left a recommendation for you on any of the social networking sites, or ask him to refer your site to other potential customers.
If you are writing a blog, write about what you have done for that customer and put pictures of up it if possible. Then let your customer know and he will surely show your blog entry to colleagues and friends, spreading the word about whatever service or product you do and how well you do it.
Word of mouth is proven to work well, and social networking is a powerful tool for keep spreading the word about your business.