Before using keywords for your site, it is always better to check for popularity of these sub theme keywords. Some or all of tools mentioned in keywords tools section could be utilized to measure popularity of these keywords. Based on popularity count of these tools we should come up with a descending order listing of our most unused but good key phrase. These are our good target keywords. As competition increases on keywords, deeper optimization then just building keyword specific pages will have to be done.
Variations on sub- theme words:
This is word- play to get into mind of user.
Now our set of 25 to 30 keywords will be expanded to include singular-plural word combinations, juxtaposing same words in a different combination, using synonyms, building on list of words using Thesaurus & a good dictionary.
The ideal set of keywords/ key phrases is to come up with around 70-100 possible ways of looking for that web site on search engines (our keyphrases)
Research on these variations of sub theme keywords for actually combing up with combinations that are relatively un optimized for yet popular. At end of this exercise we will have ranked list of keywords, which we can start optimizing for.
General observations & other nuggets:
When using google to check for competing pages through SERP house keyphrase in quotes. This will do exact phrase searching for phrase that we are optimizing for. Now to have a real feel of actual competition on this phrase use adword tool.
Typically offline competition for business & online competition are not equivalent. The client needs to be driven out of this mindset. Online competition for us depends on key-phrases that we choose rather then industry or competition chosen keywords.
Another useful tip is to watch out for ranking of subpages on SERPS page.
A higher occurenec of a sub- page suggests a lesser competitive key- phrase.
Keep excel sheets handy to work out on your key words
Here is a benchmark: If site is fairly well optimized, and has a focused theme, then combined total number of visitors from secondary variations of main keyword phrase, should be higher than number of visitors from your main phrase by itself.