I am early in the process of finding keywords to optimize each page of my high end plastic surgery site. I am trying to find keywords that are both geo targeted and include the service, but wanted input on how to find out if these keywords are highly competitive and how often they are searched on.
A quick measure of competition would be to see how many other websites contained the phrase you are interested in, e.g. compare the number of results for a search for "some competition" [google.com] with one for "not at all competitive" [google.com].
Of course, much more significant than those numbers is whether or not the words and phrases are relevant to your pages, and likely to send you the right kinds of visitors. This is as much a matter of judgement as statistics.
I've been using my keyword Quality Score in Google Adwords to assist in determining which keywords a given page is best optimized for. I don't use it as the end-all-be-all, but it does shed some additional light on things.
Try plugging those keywords into a miscellaneous ad group and check the quality score. Might give you some additional insight!
There are some phrases that are used relatively frequently by users that one would never guess. Such phrases can be gold mines, and you can often corner the market on them with very little effort.
I am reminded of trying to figure out why my kid's Honda was having intermittant starting problems. Many people have had the same problem, and use similar searches to find the answer. The answer lies under a 3 word search term that only returns 600k pages.
I am aware of another highly searched term (though fairly seasonal) of only two words that returns only 478k responses. We have ranked between 1 and 5 for the past three years. These are the most accessed pages on the site.