In order to be listed in the search engines, your most important content should be in HTML text format. Images, Flash files, Java applets, and other non-text content are often ignored or devalued by search engine spiders, despite advances in crawling technology. The easiest way to ensure that the words and phrases you display to your visitors are visible to search engines is to place it in the HTML text on the page.
Just as search engines need to see content in order to list pages in their massive keyword-based indices, they also need to see links in order to find the content. A crawlable link structure - one that lets search engine spiders browse the pathways of a website - is vital in order to find all of the pages on a website.
Any web page is made of of certain key areas
1) The header element, comprised of elements such as title, description, and other ‘administrative’ elements. Basically while hidden from the viewer these elements appear in search engine results so the correct formatting and content of this area is crucial to both good SEO as well as such things as page speed, which is also now a factor in determining rankings, although at present not a major one.
2) The ‘body’ of the page, the area where the content goes, images, text, navigation links, and anything else the visitor sees, basically the bit you are looking at now.
So, good SEO is not something in isolation, it should be built into the page from planning, the esign and through to the build. Good code and good page structure are now taken into account, even o the extent of Google now starting to ’flag’ a site as mobile friendly in result listings