title: How to use OnDestroy properly
body: <p>I've seen a lot of question related to ngOnDestroy. I think many of us not using it correctly or not using it at all. <br>I just want to see a list of tips how can you properly use ngOnDestroy and what should we do in the best scenario to prevent memory leaks, speed up and optimize web apps.
  <br>What do you must to do in every case when you use it?(What are the steps you MUST to take?)
  <br>How far you need to go if you want to do it perfectly? Nullifying all references etc.</p>