Your content is your best source of keywords you may include in your meta data. Make sure, you content does not repeat itself from one page to another. Carefully research keywords before building your content - you need narrowed keywords that are achievable for the page like yours and have high monthly search volume. Single or Plural DOES matter. Same Keyword may have a high monthly search volume in plural, and a low one - in single variation. Letter capitalizing does not matter at all. Make sure you are not using trademarked keywords, or you might be punished for doing so.
