In order to pass this test you must create and properly install a robots.txt file.
For this, you can use any program that produces a text file or you can use an online tool (Google Webmaster Tools has this feature).
Remember to use all lower case for the filename: robots.txt, not ROBOTS.TXT.
A simple robots.txt file looks like this:

User-agent: *
Disallow: /cgi-bin/
Disallow: /images/
Disallow: /pages/thankyou.html

This would block all search engine robots from visiting "cgi-bin" and "images" directories and the page "http://www.yoursite.com/pages/thankyou.html"

TIPS:

• You need a separate Disallow line for every URL prefix you want to exclude
• You may not have blank lines in a record because they are used to delimit multiple records
• Notice that before the Disallow command, you have the command: User-agent: *. The User-agent: part specifies which robot you want to block. Major known crawlers are: Googlebot (Google), Googlebot-Image (Google Image Search), Baiduspider (Baidu), Bingbot (Bing)
• One important thing to know if you are creating your own robots.txt file is that although the wildcard (*) is used in the User-agent line (meaning "any robot"), it is not allowed in the Disallow line.
• Regular expressions are not supported in either the User-agent or Disallow lines

Once you have your robots.txt file, you can upload it in the top-level directory of your web server. After that, make sure you set the permissions on the file so that visitors (like search engines) can read it.

In order to pass this test you must create a sitemap.xml file for your website. Some of the best practices are listed below:

• It is strongly recommended that you place your sitemap at the root directory of your website: http://yourwebsite.com/sitemap.xml But in some situations, you may want to produce different sitemaps for different paths on your site (e.g., security permission issues)
• Sitemaps should be no larger than 10MB (10,485,760 bytes) and can contain a maximum of 50,000 URLs. This means that if your site contains more than 50,000 URLs or your sitemap is bigger than 10MB, you must create multiple sitemap files and use a Sitemap index file
• All URLs listed in the sitemap must reside on the same host as the sitemap. For instance, if the sitemap is located at http://www.yourwebsite.com/sitemap.xml, it can't include URLs from http://subdomain.yourwebsite.com
• Once you have created your sitemap, let search engines know about it by submitting directly to them, pinging them, or adding the sitemap location to your robots.txt file
• Sitemaps can be compressed using gzip, reducing bandwidth consumption

sitemap.xml example:

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<url>
 <loc>http://www.yourwebsite.com</loc>
 <lastmod>2013-01-01</lastmod>
 <changefreq>weekly</changefreq>
 <priority>0.9</priority>
</url>
<url>
 <loc>http://www.yourwebsite.com/articles/100</loc>
 <changefreq>weekly</changefreq>
</url>
<url>
 <loc>http://www.yourwebsite.com/articles/101</loc>
 <lastmod>2013-01-02</lastmod>
 <changefreq>weekly</changefreq>
</url>
<url>
 <loc>http://www.yourwebsite.com/articles/102</loc>
 <lastmod>2013-01-02T13:00:12+00:00</lastmod>
 <priority>0.5</priority>
</url>
</urlset>

In order to pass this test you must add an alt attribute to every <img> tag used into your webpage.
An image with an alternate text specified is inserted using the following HTML line:

<img src="image.png" alt="text_to_describe_your_image">

Remember that the point of alt text is to provide the same functional information that a visual user would see. Search engines, users who disabled images in their browsers and other agents who are unable to see the images on your webpage can read the alt attributes assigned to the image since they cannot view it.

Learn more about optimizing images for SEO.

In order to reduce the number of HTTP requests, you can use the HTTP Expires header to set an expiration time for your images or any other content type. You can add the following lines into your .htaccess file:

<IfModule mod_expires.c>
    ExpiresActive on
 
    ExpiresByType image/jpg "access plus 1 month"
    ExpiresByType image/jpeg "access plus 1 month"
    ExpiresByType image/gif "access plus 1 month"
    ExpiresByType image/png "access plus 1 month"
</IfModule>

In order to pass this test you must consider using a 301 re-write rule in your .htaccess file so that both addresses (http://example.com and http://www.example.com) resolve to the same URL.
- If you want to redirect http://www.example.com to http://example.com, you can use this:

RewriteCond %{HTTP_HOST} ^www\.example\.com$
RewriteRule ^/?$ "http\:\/\/example\.com\/" [R=301,L]

- If you want to redirect http://example.com to http://www.example.com, you can use this:

RewriteCond %{HTTP_HOST} !^www.example.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301]

Note that you must put the above lines somewhere after RewriteEngine On line.

Media queries allow you to style elements for specific devices (smartphones, tablets, desktop computers) by using attributes like width, height, resolution, aspect ratio, orientation or color. By using media queries, presentations can be tailored to a specific range of output devices without changing the content itself.
Example:

<link rel="stylesheet" media="screen and (min-width: 480px) and (max-width: 960px)" 
href="480-960.css" />
 
<!-- OR -->
@media screen and (min-width: 480px) and (max-width: 960px) {
    #header {
        display: none;
    }
}

An @media rule specifies the target media types of a set of statements. In the example above, we are specifying the media type screen. The max-width and min-width features are telling the browser that at any screen size larger than 480px, but smaller than 960px, hide any elements with id="header".