1. Use Cache Properly
    The most effective way to speed up a Drupal website is by properly using cache. Drupal provides some powerful caching even if no extra modules are enabled. Drupal users would know that the cache system stores a copy of the visited pages in an accessible location. After a page is viewed, it is cached and the same page loads more quickly for all the subsequent visitors.
  2. There are two core internal caching modules enabled by default. They are:

The Internal Page Cache Module: This module caches pages for unknown users in the database. The pages visited by anonymous users are saved for the first time and then reused for subsequent visitors.

The Internal Dynamic Page Cache Module: The Internal Dynamic Page cache module is a new feature added to Drupal 8 and aims at speeding up the site for both unknown and logged-in users. Extra caching layers like Varnish or Redis is also added by several seasoned Drupal site builders to increase the speed of their websites.

Recently, Drupal 8 developers have added the BigPipe demo module, which has borrowed and implemented ideas from Facebook. BigPipe allows websites to show personalized content easier and faster.

3. Bandwidth Optimization
Drupal 8 has done away with “compress cached pages”. On the other hand, it has introduced a default setting that optimizes external resources. The optimization reduces both the size and the number of requests made to your website. Drupal 8 makes it simple to aggregate CSS and JavaScript files so that they load together. On the Live environment, enable Aggregate and compress CSS files/ JavaScript files. This reduces the number of HTTP requests and the amount of data transferred.

4. Image Size
The image size you choose can have a tremendous impact on your website’s speed and performance. Luckily, Drupal 8 core offers tools to control and optimize image sizes. Use the Image Styles feature to have different image sizes for different devices like tablets and mobiles.

5. Remove Unused Modules
The last thing that you can do to speed up your Drupal 8 website is to uninstall unused modules. Drupal has changed the process of removing modules, so read about it before you start uninstalling modules.