Janine, I really don't think it's an exact science. I don't think there's a recipe that will definitely produce the results you seek. It's more that if your keywords are clearly reflected in your article, that's evidence to Google that the article really is relevant to the keywords and thus deserves higher placement.

Yes, ideally, you might have keywords in the title, the body, the conclusion, and the summary. Actually, I'd make sure they appear in the body, conclusion, and summary; and then use them in the title if it sounds right. Subtitles are good places for keywords, too. Using them in headings is effective, and in image alt tags.

How many? Just a few. I wouldn't obsess about it at all. Clear, concise writing, with well-placed keywords is all that's required.

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Mary H. Ruth/Virtual Writing & Communications
http://www.writingVA.com