Google has a great free tool for researching keywords and phrases. Google Trends is completely free and very powerful. Here’s a quick tutorial on how to get started.
Create a list of keywords and phrases that are important to growth for your product/service. Categorize that list and add some comparisons (i.e. red scooter, blue scooter)
Go to http://trends.google.com and enter the first comparison. Be sure to choose your region. Be sure to choose the correct type of keyword in the comparison. (search term vs. Topic) Compare like types.
Look at both the “rising” and “top” view in the results. When you find some new phrases that you haven’t used, start to incorporate them into your content.
Bonus Tip: If you find a real gem, make a YouTube video that includes the keywords and embed into your website page.