The program that is used by a particular search engine may vary from another search engine but both will have many protocols that have to be satisfied before a web page can be selected, then it assigns a percentage of relevancy to all the pages and the one that has the highest relevancy is display in the first position. The protocols, areas of concern that the search engine may look at are the domain name, subfolders names, file names, titles, meta tags, alt tags, headers, comments and the page content to make its decision about a page's relevancy. There are hundreds of books written about this, but for now this should give your a little insight as to the importance of understanding how each search engines program works. Designing graphics for the web is different than designing for brochures. It is as time consuming as brochure graphics, requiring an artist talent, and software expertise, but it also requires a lot of compromise in quality because of load times.
Load time is very important both for the spider timeout settings and customer patience.
In the case of the spider, if it times out, it leaves without indexing your web page and if the customer reaches their timeout setting, you lose too. If you place high on the search engine results, the first two sentences on your web site become the next most important area to be concerned with. Make them the best you've ever written, full of emotion and motivating. Even though many of the search engines are ignoring the meta tags now, I still use the first two sentences for the meta description. And don't forget about the text that is in front of your first two sentences, you may never see your sentences in your search engine description and that could be costly.