Ron Jones at ClickZ wrote a fantastic article which breaks down how to get started measuring social media, by categorizing different outcomes and their corresponding measurements.

For small businesses, I’m not sure all of these are applicable, as it may take more time to measure than benefit gained from knowing the results. So don’t get hung up on daily, or even weekly monitoring. In fact, doing quarterly assessments is a great way to bench mark your long term growth in social media. Hubspot and some other companies have complimentary tools and checklists for evaluating how well you are covering social media, and Ron’s article will help you translate those results into some meaningful metrics.

Additionally, I suggest keeping a log of your most memorable successes and failures and producing a quarterly social media report which highlights your quarter from a narrative perspective (supplemented by metrics of course). It should outline what you accomplished and why it was important. You’ll also want to map out your upcoming quarter’s plans.

Here’s Ron’s article: http://www.clickz.com/clickz/column/2102934/measure-social-media