Google Page Speed Insight Rules:

0. Install Google Page Speed Module

Google’s pagespeed module gives you a number of tools that can speed up front-end performance by making minor tweaks (trimming the domain out of local URLs, inserting DNS prefetch tags, collapsing whitespace) or major ones (lazy-loading images)

1. Avoid Landing Page Redirects

Avoid having more than one redirects from the given url to the final landing page.

2. Enable Compression

Enable that the assets served to clients are in gzip compression.

• Use Rack::Deflater
• Use Nginx Config
• Gzipping font files

3. Improving Server Response Time

Ensure that the server response time is not more than 200 ms.

• Analyse application logic and response from server, and fix the source that gives a slow server response time.
• Use Rack Mini Profiler to check the page speed and server response time.
• Avoid bad requests.
• Use CDN to host images & other static assets.
• Use SPDY on Rails
• Use Rails Caching - Refer to Rails Official Guide and Blog - Complete guide on Rails Caching.

4. Leverage browser caching

Ensure that the response from server includes caching headers or the resources are specified to be cached for only a short time.

• Move favicon.ico to assets folder and use favicon_link_tag.
• Use the following Nginx config to ensure http cache-control on images in /public/images directory:

# Media: images, icons, video, audio, HTC
location ~* \.(?:jpg|jpeg|gif|png|ico|cur|gz|svg|svgz|mp4|ogg|ogv|webm|htc)$ {
  expires 1M;
  access_log off;
  add_header Cache-Control "public";
}

• If enable Gzip compression and want to use Rails Http Caching, upgrade to nginx 1.7.3 or higher, and use Rails weak etags gem. The reason is that Nginx strip etags by default. More details: Rails & Weak ETags
• Check above point if want to use Rails HTTP Caching. Configure Rails to validate cached responses with ETags (Conditional HTTP Caching).
  • Introduction to Conditional HTTP Caching wit h Rails
  • How etags works in Rails
  • RailsCast - HTTP Caching

5. Minify Assets (CSS, and JavaScript)

Ensure that the CSS and JavaScript assets could be reduced through minification.

• minify your CSS, and JavaScript resources. This is done by default through sprockets and uglifier in Rails.

6. Optimize Images

Reduce the filesize of ithe images without significantly impacting their visual quality.

• Use Phil's Easy Optimise or Kraken.io to optimise images.
• Use progressive JPEG.

7. Optimize CSS Delivery

Avoid including render blocking external stylesheets.

• No @import calls for CSS.
• No more than one external CSS stylesheet of an reasonable size (less than 75k or so).
• Inline small CSS into HTML using style tags for above the fold content.
• No CSS in HTML things like your divs or your h1s (in element CSS).

8. Reduce the size of the above-the-fold content

Reduce network round trips that are required to render the above the fold content of the page.

• Enable Keep-Alive HTTP connection.
• Structure your HTML to load the critical, above-the-fold content first.

9. Remove Render-Blocking JavaScript

Avoid referencing a blocking external JavaScript file in the above-the-fold portion of the page.

• Use the new Typekit embeded code to load typekit asynchronously
• If using Sharethis JS plugin, Use Asynchronous Sharethis Loading instead.
• Enable asynchronous loading of scripts in Production environment:

<%= javascript_include_tag 'application', async: Rails.env.production? %>

10. Use Asynchronous Scripts

Leverage asynchronous loading of scripts.