As Per Yahoo SEO Guidelines it says that.....
Your web site should be based on quality: - It means web site should have rich content. Web site content should be original and should no be copied from other sites. Always try to write content in your own wordings.
Web site should have more pages as it can: - According to yahoo a rich content web site that have more that 100 pages fetch the attention of mostly search engines. So try to add more pages as you can in your exiting web site.
Link exchanges: - Link exchanges are very compulsory as per yahoo guidelines. Basically it is required by all most all the search engines. As many as your website have quality links, changes of a well page rank and good ranking will be more.
Update your content: - An updated site keeps have good ranking and get higher page rank provided website content should be continuously updated.
Keywords: - Yahoo still has keywords importance so fill each of your web pages with targeted keywords but not do keyword stuffing.
As Per Google SEO Guidelines it says that.....
Rich content: - Design your web site with rich and quality content. Google says that your content quality should be unique that describe your product well. Content should not be copied from other side. A Unique content rich site well optimized in Google.
Product information- Content quality should be accurate and as per your product. It shout be clear and easy to understand as per visitor point of view.
Title tag: - Google give high importance to title of your web page. So try to make unique and descriptive title that can cover your mostly targeted keywords in it but should not go beyond the given limit.
Description tag: - After title tag Google give importance to description tag so unique description for each page of your web site. It should not be same in two or more pages; it may result in supplemental issue due to content duplicity.
Broken links: - if your sit have any broken link than it can create a problem for search engines spiders. So check your web site urls.
Images V Text: - Google gives more importance to text as compare to images. Therefore use text instead of images to describe product title or important names or links.
Alt Tag : - Alt tag should be descriptive and accurate that best describe your product and services. Alt tag should not be stuffed with keywords.
Static and Dynamic: - Spiders find ease in crawling a site that is of static nature. Spiders finds difficulties in indexing a dynamic website and the problem comes when it comes at url which contain symbols like "?" instead of text. It is very difficult for spiders to keep it in its database. On the other hand a static web site a easily crawled and indexed by all the spiders.
Keyword density: - Check key word density of targeted keyword in web page content. It should be not be access.
Text Link hierarchy: - Make suitable and well text link hierarchy that user san easily view and understand better. If websites all links are in proper order than it will give and easy excess of user desired web page. No one wants trouble in searching out desired pages.
Limit year link less than 100:- as per Google quantity of links on a given web page should be under 100 and not more than that.
As Per MSN SEO Guidelines it says that.....
Keywords: - Keywords plays an importance role for web site optimization in MSN, so never forget keywords significance which is less in Google but more in yahoo and MSN.
Content: - Apart from Google MSN loves keywords density so plays good quantity of keywords phrases between your content. But in Google it is considered span placing more keywords above limit. MSN also loves fresh contents as Google.
On page Optimization: - MSN give more emphasis for "on page optimization techniques "rather than off page optimization. So if you want to rank well your site in MSN than concentrate more for "on page optimization techniques", but don't forget to do off page optimization along with as it is required by all the search engines along with MSN.
Broken link: - MSN state your web site should not have broker links so check html url links property.
robot.txt: - robot.txt file should be used for giving instructions how MSNBOt index your site in its database. Robot.txt plays equal importance in other search engines as well.
Description Tag: - Plays well descriptive content in description tag for every web page as it has great importance for both google and msn.
Content and Page Limit: - Fresh content are loved by the MSN but content limit for each and every web page should not be access the prescribed limit that is 150 kb.
Keyword sensitive: - Msn is keyword sensitive search engine so place all your targeted keywords in content and keywords tag.
Each web page should described about one topic which is good as per MSN SEO Tips and Guidelines and each page is accessible by at least one static text link.
All these three are the major search engines and your site will automatically rank.