I once read something that Tim Ferriss had said in response to a similar question. I'm heavily paraphrasing, but he was basically asked how he had so much more discipline than most others.
He responded by saying that he doesn't have more discipline - he just creates environments that decrease his opportunities to fail (ie. get distracted) and increase his likelihood to succeed (ie. finish the work).
The idea is to not trust yourself and not give yourself the opportunity to fail. A concrete example of how I've personally put this to great use in my life is how I made it a habit to go to the gym:
When I was in college, I wanted to go to the gym regularly. Unfortunately I found that when I was in my dorm room and needed to get ready for the gym, I lacked the motivation to get out of a comfortable situation. What I began doing was taking my gym clothes to class and going straight to the gym after class. This required significantly less motivation on my part because I was already walking around campus, sometimes even passing the gym by on the way back to my dorm. The step leading up to that also required very little motivation - putting clothes in your backpack. The result was that I created a sequence of events that each had a small likelihood of failure. 10 years later, going to the gym is my favorite hobby.
Another example related to getting work done came about when I was trying to work on my side projects from home. It never worked. I'd always want to browse the internet, watch tv, play video games, or spend time with my girlfriend. Starting work when my Xbox was in the next room meant summoning a monumental amount of motivation. Instead what I started doing was going to a local coffee shop or coworking space. It doesn't take that much effort to just go to a public space with wifi (and if it does, you can use the advice above). Once there, you have put yourself in an environment where everyone else is working. Aside from noise, there are fewer distractions. In addition, you'll look like an asshole if you're sitting in front of your laptop playing on Reddit for 4 hours while everyone around you is getting shit done.
If you can make a habit of completing those small triggers that lead to bigger outcomes, you'll eventually have gained a much more significant habit.