Although much of your SEO activity should, rightly, be focused on understanding what keywords and phrases you want to target and then structuring your content to go after it, there is a secondary consideration which might also be helpful.
Recently, I was writing an assessment report for a potential client on how he might improve the amount of organic search engine traffic reaching his family of websites. I had a look at the keywords that were already resulting in traffic finding one of his sites and I was surprised to see a whole bunch of culinary-related phrases had resulted in quite a bit of traffic over time. The reason this was surprising was that the website was essentially nothing to do with cooking, food, recipes or anything like that. There were, however, some articles submitted that supported the main theme of the site, but which also included mention of these culinary terms.
As a result of this ‘discovery’ we are considering more comprehensive coverage of this foody theme on the site and ways in which we can convert those visitors into customers for the main website.
It is difficult to get top search engine positions for the keywords you really want, but sometimes looking at things in reverse like this can create some good opportunities, and it is quite possible to use unlikely content which has brought your traffic in to draw visitors across to, what is for you, the main reason for them being there. Food for thought perhaps?
There are a number of ways to find out what keywords people are using to find your site. All website statistics programs ought to show you. Personally, I prefer using Google Analytics.