How to set up link previews as per my choice?

You can configure how you want links to be displayed in all your chats. You can choose any one from the following three options, 

  1. View preview of all links
  2. Block preview of all links 
  3. View preview of all links, except a few (i.e. you can block up to 20 domains) 

Now to configure this, click on your Profile Picture (top right corner), and go to Settings -> Media and Links. In here, the above mentioned 3 choices will be displayed and you can choose an option that best suits your needs. 

Note: In the 3rd choice, an option to disable previews for Gifs will be provided by default. Enabling that will not display any gifs in your chat window when they are shared in conversations.