Headings don't have to be visible. You can encase your graphics that serve as headings within heading tags and use ALT tags that contain the key words for the search engines to read. You can also use heading tags within tables. Short pages that contain keywords are weighted higher in search results than long pages containing the same number of keywords. A very short page that has just one instance of a keyword may rank higher than a longer page with several instances of the keyword.
Text placed high on the page ranks higher than text placed lower in the page.
Make sure that your descriptive text, keywords, and most important information, are at the top of your page. Make your directory names and file names descriptive, without making them lengthy. Some search engines read the ALT tags within the image statement . When you have graphics, also use alt tags that describe the pictures. These ALT tags should be descriptive, containing the important keyword concepts that the graphic images convey.