You shouldn't create a keyword. There are millions of them ready to use. Each of them has its own stats (popularity, adwords cost per click, etc.), belongs to a concrete niche or market, has different variations (long tail keywords and similar words), and many more. So you need to research the niche using specialized tools like Google Keyword Tool External or, for example, some special databases like Xedant.com Keyword Database and choose keywords that are more relevant for you, have reasonable amount of searches per month and competition rate.
wow ... that is way vague. Okay, first pick a niche, then run it through google's keyword external, as Maganom said. There are tutorials all over how to use it. I then look over 4,000 seraches monthly on a broad setting and under 50,000 competition, and there are tonzzzz of keywords available. Also, it is different for sites than articles.
You need to research your keywords, not create them. Pick a general keyword on the subject, and then start drilling down with google adwords, or better yet Market Samurai.
You can search for the best keyword that can give you traffic for your site. It should be less competitive but has a higher demand.