Choosing your primary keywords may be one of the most difficult parts of good SEO. It is also, however, one of the most important. When you begin optimizing your website for search engines, you will need to choose one primary keyword or keyword phrase, and four to six secondary keywords.
These keywords are going to be essential later on. You won't just use them for a single page on your website. Instead, they should feature prominently on each page of your website, in any website-related blogs, in any website-related newsletters, and in any website-related press releases. SEO goes beyond just a website.
With that in mind, look for keywords that will stand the test of time. Avoid keywords that are too general; you want targeted keywords for targeted traffic. But don't swerve to the opposite extreme; a keyword is no good if it's something so specific that no one would ever search for it.
Your secondary keywords can be a little more flexible than your primary keyword or keyword phrase. Pick the words people are most likely to use when searching for your product or information. You should ideally have between four and six secondary keywords, but if necessary, pick as many as ten. Don't go above ten, as too many keywords end up diluting the importance of any of your keywords.
Look for a blend of general and specific secondary keywords. Better yet, make one or two of them keyphrases, such as "handcrafted knit scarves" that blend the specifics of the three words together with the generalness of each individual word.
Once you have your keywords, don't limit them to just your website. Use your primary keyword phrase every time you link to your website, in blogs, in newsletters, and in RSS feeds. Don't overlook relevant forum signatures! The right keywords, used in the right way, can be invaluable.