DO:
Be informative. The surest way to get search engines to index your site is to use clear, relevant and specific language. This reveals your site as it was made to be seen while avoiding ambiguities. As a result, in any given search the author-audience relationship will be that much tighter.
Use constant and consistent thematic keywords. Each and every site has an underlying "big picture". Try to capture the meaning of the site in a few critical words. Refer to these same words in the body of the page (or in other heading sections). Most search engines give more weight to words found in the title, especially if those words are also found in the body of the text.
Use meta tags. This helps you control your site’s description in the search engines that support them. Require that each page have a meta description tag, and that the content of this tag is in the first two or three sentences of the main body copy.
Position your keywords. Be sure your strategic keywords appear in the crucial locations on your web pages. The page title is most important. Failure to put strategic keywords in the page title is the main reason why perfectly relevant web pages may be poorly ranked. Search engines also like pages where keywords appear "high" on the page. To accommodate them, use your strategic keywords for your page headline, if possible. Have them also appear in the first paragraphs of your web page.
Use alt tags. These provide alternative text for all images. Make the alternative text rich and meaningful. Adding alt text should be standard procedure for all web page creation. This is very important for those surfers that have graphics turned off to save time as an ALT tag will display if the graphic does not.
DON’T:
Do not abuse meta tags. The inordinate use of meta tags is not only frowned upon, it is self-defeating. The window of opportunity for this little prank is closing. Most of the major search engines have refined their search capabilities to ignore excessively long meta tags and some are now penalizing sites that use them.
Avoid keywords that do not relate to the site.
Avoid duplication of pages with different URLs.
Do not use different pages that bridge to the same URL
Where possible avoid using frames for your page, or at least your main home page.
Do not repeat a word excessively. In a meta tag, a word in the same form should not appear more that 3 times.