ROI is Return on Investment, it is used to know about the efficiency of your investments and to calculate it. It can be calculated by diminishing your investment costs from gain of investments and it gets divided by the actual cost of investment.
Some of the people in this thread seem to think you're talking about your SEO PageRank (building backlinks, etc.)
AdWords "rank" is Quality Score, and it based on your bid and CTR. Create very targeted ads that reuse keywords you're bidding on (because then the keywords in the ad will appear in bold). Create lots of niche ad groups so that you can segment ads with targeted keywords.
You can submit your website to search engines. Google really likes Sites that keep their content fresh and unique. The more you post, the more Google will crawl your site and the more chances for you to increase page rank.