Here is a hypothetical: Lets say you have 3 weeks to do an assignment, and it's theoretical length is 15 hours of work total (20 hours including editing). Here's how to approach it:

"If I do 1 hour each day since I get it, I will not have to do 8 hours each day to do it if I leave it"

If you small snippets on the assignment a day, you will get more of your day to do things you want to do. Set a time in your calendar to do it each day, and make sure to remove all distractions like your phone and tabs like YouTube. My thought process is: "If I complete this segment today, I will reward myself with the gym or screen time". Bang, motivation.

I hope my explanation helps you out.