For the proper display of your site
 
 
 
Proper HTML code: Many search engines cannot properly catalog or index a site that has HTML errors. This reduces the amount of traffic your web site receives from search engines. If you want your site listed on search engines then make sure that you have correct HTML code. 
Search engine: The search engine is equivalent of a version 2 browser. It cannot read flash, DHTML, JavaScript and dynamic pages even having trouble at times with frames. Search engines may have difficulty in crawling, indexing, and extracting the content of your site if you have broken HTML. The lowest form of "browser" is the search engine.
Key HTML components: The key components are titles, descriptions, visible text, alt image tags etc. If you don't find them because of typos or other mistakes, the spiders may leave them without reading the content of the page. Search engines score a page by looking for relevant terms in key HTML components of specific places within a document. 
Proper document structure:  Poor document structure like META tag placed in the BODY section of the page instead of the HEAD section can cause the spider to ignore the tag and cost you a good ranking. 
Clear title: TITLE tags are very important to search engines. If you are tired and under deadline to get a new page up, you might have typed TILTE instead of TITLE for your TITLE tag. If you have made such little error the search engine will ignore all of the content of the title tag. 
Proper page and content: The search engines should be able to read your content that contains your keywords properly and clearly. And the off page factors like inbound links are excluded from it. That means if you create the page and content properly then  it is much easier for the search engines. 
Use of Internet Explorer: Internet Explorer is much adjustable for the mistakes in code. By building only for IE you are creating for the most error forgiving browser ever. Thinking of a search engine which browses your site like Internet Explorer 6 is a dream. If the site do not display right in Netscape, Fire fox, Opera or an old version of Internet Explorer, the search engines cannot read it.