i use keyword that match my product and service.if you publishing a web page then your keyword should have to match with you page constants and other services.
I've learned that you've got to use one suited to your niche. I used Market Samurai but it took too long to load cause of the # of modules included. I mentioned this to the support staff. There's KeywordSpy, Keyword Elite et. al. that some folks like. There's NicheFinder and TrafficTravis (which is free). Some folks use a mix and find the best low-hanging fruit -- keywords with lowest competition but high searches. Be Free