Select unique title for your article,
Search the same article title in Search engine. If your article title matches with the search results articles, then your article considered as duplicate, so avoid adding duplicate contents to the website.
Yes i agree with the last post, you need to have good contents in your site, content is king always, If you have good quality contents, when search engine sees your content so unique then it will be ranked higher in the search engines.
I have no idea of finding the most keywords used per day, but you can search most popular keywords through Google Adwords, Google Adwords tool is best tool to search particular keywords for your website.
Increase visitors using the social media marketing techniques, create a fan page in twitter as well as in facebook, this will provide you the huge traffic.
I have been in Ecommerce online business since 2 years, this is good experience for me to share some good points and get some knowledge through this forum site.