jakebohall - 3:19 pm on May 23, 2013 (gmt 0)
Do a download of all your backlinks from GWT. Then look through each one to see if it is defensible as a "natural" link, or if it is an obvious link for seo. If you have a lot of spammy links, you might consider a cleanup effort. There are several tools out there that can help you remove bad backlinks.
One thing to be particularly mindful of is using keyword specific anchor text, as this was known to create issues with the first penguin update.
Definitely follow Martini's advice about looking at how your rankings have shifted, and don't get too knee-jerk if the impact seems minimal.