The greatest writers of our time all share one thing in common: They were disciplined and wrote every single day, which is another way of saying that they all had developed routines that enabled them to become as good as they were. Much in the same way that you won't be a great musician or sports player without practicing daily, you won't become a great writer without writing daily. Routine, therefore, is a necessary component to becoming a good writer, and it's for this reason that the notion of "just write" is so often recycled throughout the writing community.

That in mind, your number one goal as a writer should be to develop a routine that'll result in you writing at the same time every single day. You consequently need to be aware of all of the bad habits you have that might get in the way of writing, be it watching TV or being on reddit for hours on end. Once you're aware of those distractions, the burden falls on you to devise a game plan so that you can counter them and create good habits to replace them.

So for example, I know that I can't write in my room: there's just too many ways for me to get distracted there, plus my office chair isn't comfortable after a while. So I write in the dining room or the library or a coffee shop, and I set reminders on my phone so that I write in these places at or near the same time every day.

And sure, sometimes you won't know what to write at all and might find yourself stuck. That's when you go through your old notes, edit stuff you wrote before, revisit old stories, and tweak around with what you already have. Reading is also something else I do to offset writer's block since it gets my creative juices going again. All that in mind, when it's my time to write, I go to a place in which I can be the most productive and write something just to get in the habit of doing it. Then it becomes easier. That's how the brain works.

TL;DR: You can't be great at something unless you practice every single day at it. That said, if you want to be a good writer, develop a routine, go to a place in which you have the least amount of distractions, and stick to that routine until writing at the same time every day becomes second nature.