Smith Brothers Media HAVE YOU BEEN HIT BY PENGUIN 3.0?
Google Analytics: This tool will allow you to monitor your search traffic in real time and track any sudden rises and drops. Penguin was released on around the 17th of October, so pay extra attention to that particular weekend.
Incognito Mode: Ctrl+shift+N will open up incognito mode in Google Chrome, giving you a view of your search rankings that isn't skewed by cookies or previous searches. Google can often distort searches due to an attempt to give you what it thinks you want, so try searching incognito for the real story.
Keywords: Pick out a few keywords that previously worked well for you in the past and see where they appear on the first few pages of a Google search. If they're significantly lower than they used to be, there's a good chance that they're been penalised.
It's not always immediately obvious when your site has fallen in the rankings, and it can be even more difficult to find out why. To get the full picture, contact the team at Smith Brothers Media.