How to use breakpoints in drupal 8?

There we have simple way to use breakpoints means separate media query in drupal 8 and that will also help in speed up or optimize the website.
We have some following points, that will easily clear your doubts about breakpoints and separate media query.
1. We will create a file with the name of 'yourthemeORmoduleName.breakpoints.yml', Example for theme like your theme name is 'bartik' the file name will be 'bartik.breakpoints.yml'.
2. This breakpoints file will be use for write the code of media query for responsiveness. This file will be located in 'themes/bartik/' root.
Example:
bartik.mobile:
  label: mobile
  mediaQuery: ''
  weight: 0
  multipliers:
    - 1x
    - 1.5x
    - 2x    
bartik.narrow:
  label: narrow
  mediaQuery: 'all and (min-width: 560px) and (max-width: 850px)'
  weight: 1
  multipliers:
    - 1x
    - 1.5x
    - 2x    
bartik.wide:
  label: wide
  mediaQuery: 'all and (min-width: 851px)'
  weight: 2
  multipliers:
    - 1x
    - 1.5x
    - 2x    
bartik.small:
  label: small
  mediaQuery: "(min-width: 0px)"
  weight: 1
  multipliers:
    - 1x
    - 1.5x
    - 2x
bartik.medium:
  label: medium
  mediaQuery: "(min-width: 768px)"
  weight: 2
  multipliers:
    - 1x
    - 1.5x
    - 2x
bartik.large:
  label: large
  mediaQuery: "(min-width: 1024px)"
  weight: 3
  multipliers:
    - 1x
    - 1.5x
    - 2x
Here the breakpoint properties are:
    Very first we will take a unique breakpoint name like: bartik.small:      (moduleName/themeName.unique breakpointName),
    Example: bartik.small: ,bartik.medium: ,bartik.large: ,bartik.wide: ,bartik.narrow: ,bartik.mobile:
   
    label - The human readable name of the breakpoint
    mediaQuery - a valid @media query(for responsiveness)
    weight - where the breakpoint is ordered in relation to other breakpoints
    multiplier - the ratio between the physical pixel size of the active device and the device-independent pixel size
               - 1x
               - 1.5x // supports Android
               - 2x  // supports Mac retina display
              
3. After that we will create new library and attach this breakpoints in 'bartik.libraries.yml' file.
Syntax:
libraryName:
  version: 1.0
  css:
    theme:
      css/desktop-small.css: { media: all and (min-width: 851px) }
      css/mobile.css: { media: only screen and (max-width: 767px) }
      css/mobile-common.css: { media: all and (min-width: 560px) and (max-width: 850px) }
     
    Same like we can create many viewports / breakpoints / media queries and attach with libraries and templates of our website.

4. Now this specific library we will render on template where we want to apply.
Example: {{ attach_library('mythemeName/libraryName') }}   

So in this way we can optimize the site and increase the performance with the help of breakpoints because with the help of this only in case of Mobile or Tab or Ipad or Desktop specific mentioned css will be rendered else not.
And the most important thing is clear the Cache and run Cron.

Note: If have any suggestions or issue regarding 'How to use breakpoints in drupal 8?' then you can ask by comments.  

How to optimize the website in drupal 8 ?

Sometimes we create the website but that is not quickly responded and we don't get proper users response on site. Sometime our client want to Speed Up the website and we just go through the Admin section and Aggregate CSS and JS files. But that is not properly working as our expectation. So here very first time we have some suggestion in easy way to Speed up the website and that will surly Speed up our website . That is tested with our projects. Please have a look suggestions for Desktop and Mobile both end..

Suggestions:
- Module to speed up site(Image Lazyloader, ADVANCED CSS/JS AGGREGATION)  --> We have added screen shot for checked options.
- Aggregated CSS/JS code.
- Remove extra CSS/JS that is not use full for front page.
- Set required custom image size(image styling) for page images.
- Create custom size of images(Home -> Administration -> Configuration -> Media -> Add image style).
- Follow Google page speed suggestion.
- Reduces Request to server.
- Uninstall extra modules.
- Use Optimized Image.
- Use critical css only ,use only those css/js which you need most.
- Add Async and defer attribute.
- Eliminate render-blocking resources.

Note: If have any suggestions or issue regarding 'How to optimize the website in drupal 8 ?' then you can ask by comments.