Top 21 SEO DOs:

1. Make changes that benefit users. Focus on the user and all else (including rankings) will follow.
2. Create and maintain sensible and consistent navigation paths.
3. Be continually aware that each and every page on your site is a potential customer entry point. Think laterally.
4. Label each and every page clearly; describing its content in words your users would most likely employ.
5. Pay attention to detail. Google takes hundreds of factors into account when ranking web pages, and so should you.
6. Continually create content that your users will find beneficial.
7. Inform the search engines of new pages added to your site by submitting sitemaps and providing spider paths.
8. Use text to qualify or augment non-textual content such as images or videos.
9. Continually educate colleagues and collaborate with them in regard to SEO techniques.
10. Continually use data to analyze the impact of SEO techniques.
11. Streamline your code to make it as lightweight and elegant as possible.
12. Ensure there’s one page that is a champion for each of your most important keywords.
13. Pursue direct links from relevant sites aggressively.
14. Insist on site map diagrams and wireframes when developing or reworking templates, sections or sites.
15. Utilize hierarchal structures whenever possible, from individual pages to folder nesting to site navigation.
16. Use CSS liberally and JavaScript sparingly.
17. Be patient. Good rankings take time; quickly-won rankings almost always evaporate.
18. Be transparent with your results: there are no bad rankings, only opportunities for improvement.
19. Remember that everyone associated with your business is a potential link partner, including your customers, your affiliates and your advertising partners.
20. Take the time to read blogs, participate and forums and stay on top of developments in the SEO world. Search engines are dynamic.
21. Research,Research and Research.

Top 21 SEO DON’Ts:

1. Don’t make changes for improved search rankings that negatively impact a user’s experience. The user comes first.
2. Don’t duplicate content, knowingly or through technical carelessness.
3. Don’t use parameters that become part of a page’s permanent URL structure.
4. Don’t create a page that is not linked to an appropriate parent page.
5. Don’t knowingly let a page 404 (file not found). Redirect dead pages to new pages relevant to that old page.
6. Don’t use Flash when HTML can achieve the same user experience.
7. Don’t make your users search for categories: provide a click path.
8. Don’t give away your link love without good reason (i.e., a benefit).
9. Don’t put pages in competition with one another for your most important keywords.
10. Don’t use gray- or black-hat techniques that could put your search engine rankings at risk.
11. Don’t deploy SEO improvements en masse. When possible, roll out changes incrementally.
12. Don’t rely on top-down navigation to direct users to content. Think laterally.
13. Don’t put content in pop-ups.
14. Don’t use splash pages.
15. Don’t use coding techniques that are less than optimal for SEO just because they’re easy.
16. Don’t trust vendors about SEO issues. Their intention is to sell a product, not to improve your search engine rankings. As often as not, vendor SEO “solutions” cause SEO problems.
17. Don’t panic when your rankings take a hit. Rankings fluctuate, and if your rankings don’t bounce back quickly, a considered strategy will work better than a band aid.
18. Don’t take the search engines’ advice at face value.
19. Don’t rely on anecdotal or even expert advice in making keyword selection choices. Use data.
20. Don’t put off until tomorrow what should have been done yesterday. It takes long enough to rise in the search engine rankings, so any delay is amplified.
21. Don’t say “I do SEO”.

Reference : SEOSKEPTICS.com

SEO Duplicate Content: There is a myth among SEO professionals called Google penalty for duplicate content. Many SEO professionals say that Google penalizes sites that have duplicate content. This information does not follow! There is duplicate content within a site, duplicate content on the network, such as news, for example, and copying content, ie, theft of content.
Duplicate content within the site:
Most of the time you provide the same content on different URLs, as is the case of an e-commerce, for example, that uses session IDs.

For example:

• http://www.example.com
• https://www.example.com
• http://www.example.com/index.htm
• https://www.example.com/index.htm
• http://example.com
• https://example.com
• http://example.com/index.htm
• https://example.com/index.htm
• https://example.com/index.htm

To resolve this problem you can choose the URL of your own, that you really want to appear in the search and do a 301 redirect to other URLs so that all just point to the URL you have chosen. If you can not do this redirection use the rel = “canonical” for the search engines to better understand your site and its distinct URLs.
The goal is to make the search engines know that these pages have the same contents and index only one version to display them in the search results.
Can also occur in some cases, you have two pages with the same content and one of them being a version just for printing. In this case you should put a meta noindex tag in the print version. If you do not tell Google which page to be indexed will choose one of the two and he may choose exactly the print version.

Duplicate content on the network:
You can, for example, republish the post in your blog, provided you cite the source and the author has a link to the original post. This is perfectly correct, and Google will not punish you for it.
Google knows when your content is duplicated as in the examples above and will not be any punishment in such cases.
Duplicate content (theft of content):

You develop a site and someone unscrupulous uncreative copy your HTML, your pictures, finally, the entire contents of your site and will publish the contents stolen. If you discover, report it to Google and prove that this content is yours, he will be punished. But in this case since it is not duplicate content, but theft of content.
Obviously we are not talking about manipulation of the classification results using techniques of Black Hat SEO. In this case not only duplicate content, stolen and otherwise attempt to manipulate the search engines, especially Google, your site will be banned from the index!

The duplicate content problem has finally been resolved with Google’s new canonical element. Web developers can indicate their preferred page URL using a new
tag in the HTML .
For example:

<link rel=”canonical” href=http://www.example.com/ />

inside the <head> section of the duplicate content URLs:

Note:

• The canonical URL must be on the same domain, although sub-domains such as www.mysite.com and products.mysite.com are permitted.
• Relative path names are handled and Google will resolve URLs to any path set by the page’s link.
• The preferred URL does not need to contain an exact replica of the original page content. Google will permit slight differences, such as the order of a list of products. However, it is certainly advisable to avoid that situation where possible.
• Google will follow canonical chains, but recommend that a single valid URL is specified for the best results.