The most treasured use of AdWords for SEO is to lookup keywords. Keywords are the base of any SEO campaign and even if you are a pro in your niche, you should continuously research keywords just because users often search for quite unanticipated keywords and key phrases you as a pro will never consider. Nonetheless, what matters most for top rankings is which keywords your target audience is looking for, not which keywords you as a pro consider most common in a specific niche.
In order to discover what users are looking for, you need a keyword research tool. It is correct that there are several free and paid keyword research tools, but Google AdWords Keyword Tool is many years ahead of them all.
It is easy to use AdWords to search for keywords. You can either enter the URL of your site or insert some seed keywords. The tool will routinely produce a whole lot of suggested keywords. Check out the results and shortlist all the keywords that seem important and have a reasonable global search volume.
You may want to rank well for ALL the generated keywords, but it’s beneficial to put all your efforts on a certain few. The idea now is to discover keywords that are rather easy to optimize and yet have a sizeable search volume. These would be the keywords with the least competition in Google. Go to Google and put in each of your short-listed keywords. It’s best if you search for the precise phrase, so put double quotes around your keywords.
See how many web results there are for each of the phrases. Now that you have collected the “number of web results” for each keyword, compute competition ratio by dividing it’s “global search volume” by the “number of web results.” The keywords with the high ratios are the simpler ones to optimize.