One thing you should never do is pack in gratuitous repetitions of keywords or use sophomoric tricks like creating white text on a white background to hide keywords. All the major search engines know that even in well-written and edited text, keywords and phrases will make up only 5–8 percent of the number of words on the average page of text. Pages with a suspiciously high keyword rate will lose search engine ranking, and pages that use hidden word repetition tricks may be banned from mainstream search engines.
The best keyword advice for good search visibility is simple: write clear, well-edited, interesting prose, and check your page titles and the other elements above to make sure the key descriptive words or phrases are featured.