Use the words that are appropriate to the endeavor!
When you take time to write solid content, you automatically use the necessary search words.
Note what Wikipedia has to say about it:
"While an obvious goal of SEO copywriting is to cause the business's or product's web page to rank highly in a search, most experts in the field would argue that it is of secondary priority. The foremost goal of SEO copywriting is to produce succint, effectively persuasive text for a well-written web page.
Writing that 'optimizes'a search, but which offers little useful information or only weak persuasion, is frowned upon in the profession as at best ineffective. At its worst, it becomes a costly resource inducing potential buyers to turn away from the site rather than generating sales."
