An excerpt from http://www.sitepoint.com/how-to-content-audit/, by @Ilia
Most people break out in a cold sweat when they see the word “audit.”
The good news is this post is not about traditional audits. It’s actually about conducting a content audit on your website. However, just as with your personal finances, content audits are necessary and when done correctly, are extremely beneficial for your website.
Depending on the size of your website, content reviews may take up to a few hours, but the benefit you’ll reap from it will far outweigh your investment. You can use them to find and correct SEO errors, discover which practices produce the best results, and improve your content production process.
In this tutorial, you will learn everything necessary to conduct your first content audit, without reinventing the wheel. Here are the steps we will take:
You will learn how to gather primary data from sources such as Google Analytics;
Then you’ll learn how to combine the data from different sources into one spreadsheet;
Finally, you will receive tips on how to use the information you have collected in order to gain insight and find opportunities to improve your content.
All of the tools recommended in this guide are either completely free or have a trial version.
You’ll need to use spreadsheet software to collect and manipulate the information for your audit. Which provider you choose is up to you. The most popular are Microsoft Excel and Google Spreadsheets. I recommend the latter because it is free and allows you to easily pull in and manipulate data from external sources such as Google Analytics, which I show you how to do later.
However, people have complained that Google Spreadsheets tends to run slow as your spreadsheet grows. So if your site is pretty large, you may want to use Excel.