The basic SEO requirements

Here are the list of the most important SEO requirements that must be followed in each optimized page on the site. Requirements are also useful as a SEO guide for the developers of website, which will be optimized.

• Unique tag title reflects content of the page, it's optimized for the requests promoted on the page. Usually on the detailed pages of large catalog, titles are formed using specially created template using key words (buy, sell, price, shop, Moscow, cheap, other words from the serch queries statistics). Developers have to provide an ability to set the title tag on all the pages of the website manually.
• The page must contain single main header — h1. It is preferable to keep the order of headers on the page (first h1, then h2 and h3). Developers should not use headers h1–h6 as elements of design or markup and they should not be used in the text part of the page. Headers style should be described in CSS style file.
• All the images must contain alt attribute (except elements of design and markup, their alt attribute should be empty alt=""). There must be an offset between pictures and text. It will be good if the file name of the picture reflects the essence of the images (and alt tag). It is preferable if the text longer than 1 500 characters is followed by illustrating picture, the text longer than 3000 characters should be followed by two pictures. Developers should always write alt attribute of the images, it's the rules of HTML.
• Markup the text with paragraphs. Developers shoud describe style for paragraphs  in the CSS file. Usually followinf properties are set: padding, margin, font, color, other (if necessary).
• The dash and the quotation signs in the text are made using a special html-tags: — dash, « for left quote and » for right quote.
• All the styles which are used on the page twice or more times are extracted to separate CSS class. Developers sould always extract as many styles as possible to CSS files to make the code lightweight and to optimize work with styles website loading.
• The links are put from news and articles to promoting pages, they contain key phrases (don't forget to dilute anchor sheet). On average there is on ankhor pre 1 000 characters of text. Developers should describe styles for links (color, underline, etc) in CSS file.
• All pages should have human-readable URLs, they should meed two following requirements: containing of the key phrase and maximal conciseness. If you change the URL of the page, you must put 301 Redirect into .htaccess file. Developers should remember that providing human-readable URLs is of one of the most significant requirement of website optimization.
• The content should not be duplicated on another page of the site (even partially). It would be better to make unique even announcements for news and articles, but not to get them from detailed text, and not to remove one of the duplicates from indexing using Yandex tag: noindex
• External links contain attributes rel="nofollow" and target="_blank" to open them in a new tab. Also, links might be hidden with JS or AJAX. Developers can provide warnings to users, if the link is opened in a new tab.