The term optimization (Search Engine Optimization in English) means all those activities designed to increase the volume of traffic a website receives from search engines. These activities include the optimization of both the source of the page, or content.

The activity of search engine optimization techniques that include various operations are performed on the HTML pages and content of the website, as well as the overall hypertext structure.
The professional specializing in the optimization is SEO (search engine optimizer, search engine optimized). In very large sites, or particularly complex, SEO remains in close contact with the team, necessitating a second treatment of the elements of specific skills that are unlikely to fall in a single person.
Optimizing a site is functional to its ranking in the response of the engines, which in turn is dependent upon the visibility of products / services sold.

Optimization for Google
Google introduced a new element in the approach to the problem of web indexing, PageRank, algorithm evaluation of the relevance of a page based on mathematical concepts that the inventor of Ethernet, Bob Metcalfe, summarized by the term network effect: a network is the more useful the higher the number of its users. Google indexes a page based on its content and links pointing to it.

 Best practices for optimizing pages
As regards the structure of HTML, is a good idea:

Place important content at the beginning of the HTML;
Use HTML tags as possible relating to the structure of the content presented and ensure that the page code is formally valid.
Appropriately differentiate the titles of the pages of a site, make clear and consistent with the content of the page should contain the keywords more weight;
Avoid sending unnecessary or uncontrolled information (potentially harmful) by <meta>: browsers ignore them, no crawlers;
Avoid the use of JavaScript to handle the navigation, because the crawler does not interpret the script and do not follow these links. Instead, use standard links tagged with the attribute <a> <href>. The latest generation of browsers will have no trouble managing that contain either a link address in the href that a call to a JavaScript onClick event handler: if it is deemed necessary, you can insert it and it will run before connecting real . It is however also important to remember to insert the link using the href attribute to the benefit of non-standard browsers, browser accessible, and crawlers.
For the management of servers and URLs, however, you should:

If possible, choose the URL of the page to contain the keywords most likely to occur, or which is descriptive and possibly similar to the title of the page;
If possible, avoid sending any parameters for server-side application through the inclusion of a question (query) in the URL of the page, namely the presence of parameter = value pairs after a question mark after the address Page (http://www.sito.it/percorso/pagina?parametri=valori). Some search engines will download only the page and index base, regardless of the query;
Furthermore, if the query contains specific information about the session (eg session ID, which vary for each visitor), even Google gets a unique URL for the page, and can draw the most diverse of a negative. For this type of information is appropriate to use cookies;
Avoid using non-HTTP redirects (via tag <meta http-equiv="refresh">), because it is said that the search engine will follow. It is also widely thought that their presence would penalize the ranking of a page. Implement instead redirect all HTTP redirect with an answer;
Never serve different content to crawlers (Cloaking) tries to recognize the user agent string or the IP of the bot that scans our pages. It is a harmful practice that exposes the real danger of cancellation by the indexes of the engines;
Implement the sitemap.xml and robots.txt file to instruct search engine crawlers to index what content and what to exclude from indexing.

 Image Optimization
The image search is the second type of research on Google. To ensure that images are indexed and searchable by search engines, contributing to the searchability of the page where they are inserted, the image must have a url that describes the content of the image (eg / images / mobile_rosso. jpg), and there must be an ALT tag description (what appears to be descriptive of the image).

 Optimizing PDF files for
The optimization of the documents in PDF format provides some assistance when you created the file.

The most important elements to be completed correctly for positioning on the SERPs of a PDF document are:

the name of the file, if it is made up of several keys to use the hyphen to separate, for example, if the PDF file is about pets will use the following file name: animal-domestici.pdf
internal properties to the document: click on "File" - "Properties" and fill necessarily "Title", "Subject" (which would be the description), "Author" (you can put the name of the site) and "Keywords".
The title of the document: If the document does not have a title, it will be to attribute a Google. Better, then, indicate the title you want to give the document using the font: Verdana, Italic and centered.
As regards the inclusion of a link in the page, note that a pdf file is read by Google as a kind of web page in its own right and is therefore a backlink to your site. It is important to tackle questions related to the link, that is, enter the exact page reference. For example, if we have a PDF that talks about animals on a portal of animals, you'd better put the link to the page that talks about exactly those households.