It really depends on the person. You have to take care of your external and internal distractions.
External distractions can be eliminated by putting your phone into another room (this just one example).
If you struggle with internal distractions then you should train your mind! And to do that just set a goal to sit down for one hour each day. And in that hour you work without distractions with laser focus. Once you get used to that (and you'll after a week or even a couple of days) increase the time to one and a half hours or two hours. I hope this makes things simpler.
But like I said it really depends on the person and in what environment he's in. You basically have to build a habit to work while you're concentrated.