Rand Fishkin presents several great ways to kick-start your Social Media Marketing campaign.
Not only does he provide some high-level considerations to make as far as where and how your market interacts online, but also provides a great starter list of sites to begin searching for, and connecting with, your marketplace.
Each of these sites have different foci, unique benefits and demand attention to detail and a sub-strategy that considers the quirks and peculiarities of the userbase. For example, making it to the top of Reddit with a politically focused article is far easier than doing so at Digg (or Del.icio.us/popular).