Step 2: Add Keyphrases from Your Website's Log File
There's an excellent chance that your website's log file already contains a treasure trove of information about the keyphrases that your end-users searched prior to arriving at your website. That keyphrase list is guaranteed to be eye-opening. Expect some cringing.
For ease of use, most webmasters translate the website log file into easily interpreted reports, using a website statistics package such as WebTrends or the free Google Analytics utility (google.com/analytics).
In any case, ask your webmaster to generate a report which shows the keywords that attracted visitors to your website, along with their associated traffic volumes and average number of page-views.
Are any of these keyphrases generating a substantial amount of traffic? Do certain keyphrases attract users that view multiple pages before leaving your website? If so, add those keyphrases to the brainstorming list.