Google Ads operates on a pay-per-click model, in which users bid on keywords and pay for each click on their advertisements. Every time a search is initiated, Google digs into the pool of Ads advertisers and chooses a set of winners to appear in the valuable ad space on its search results page. The “winners” are chosen based on a combination of factors, including the quality and relevance of their keywords and ad campaigns, as well as the size of their keyword bids.
To a spider, www.domain.com/, domain.com/, www.domain.com/index.html and domain.com/index.html are different urls and, therefore, different pages. Surfers arrive at the site’s home page whichever of the urls are used, but spiders see them as individual urls, and it makes a difference when working out the PageRank. It is better to standardize the url you use for the site’s home page. Otherwise each url can end up with a different PageRank, whereas all of it should have gone to just one url.
Another excellent guide is Google’s “Search Engine Optimization Starter Guide.” This is a free PDF download that covers basic tips that Google provides to its own employees on how to get listed. You’ll find it here. Also well worth checking out is Moz’s “Beginner’s Guide To SEO,” which you’ll find here, and the SEO Success Pyramid from Small Business Search Marketing.