"This document first began as an effort to help teams within Google, but we thought it'd be just as useful to webmasters that are new to the topic of search engine optimization and wish to improve their sites' interaction with both users and search engines. Although this guide won't tell you any secrets that'll automatically rank your site first for queries in Google (sorry!), following the best practices outlined below will make it easier for search engines to crawl, index and understand your content.
Search engine optimization is often about making small modifications to parts of your website. When viewed individually, these changes might seem like incremental improvements, but when combined with other optimizations, they could have a noticeable impact on your site's user experience and performance in organic search results. You're likely already familiar with many of the topics in this guide, because they're essential ingredients for any web page, but you may not be making the most out of them.
Even though this guide's title contains the words "search engine", we'd like to say that you should base your optimization decisions first and foremost on what's best for the visitors of your site. They're the main consumers of your content and are using search engines to find your work. Focusing too hard on specific tweaks to gain ranking in the organic results of search engines may not deliver the desired results. Search engine optimization is about putting your site's best foot forward when it comes to visibility in search engines, but your ultimate consumers are your users, not search engines.
Your site may be smaller or larger than our example site and offer vastly different content, but the optimization topics we discuss below should apply to sites of all sizes and types. We hope our guide gives you some fresh ideas on how to improve your website, and we'd love to hear your questions, feedback, and success stories in the Google Webmaster Help Forum."
Source - Google