There are two different approaches to getting more time to write: finding time and making time.
Finding time is the lesser of the two. It implies that you have a set schedule and routine, perhaps because you’re working or have a family life or are involved in other important activities. Your job as a writer is to find the time between those activities for your writing. In this set of circumstances, you must get your schedule in front of you and simply timetable yourself into the writing chair.
This sounds obvious, but almost all the wannabe writers I’ve ever spoken to have the same problem: they are expecting Life to somehow open up a window of a few weeks so that they can ‘write the book they want to write’. Life doesn’t usually respond on its own.
If you feel trampled into apathy by the demands of the world around you, your family, your job, you will feel as though the biggest barrier to your writing is Time.
This is what you have to do regarding timetabling:
i) Take a look at your weekly schedule; examine your commitments; work out at least 3 hours a week, preferably contiguous but not vitally so, and block that out for writing. Nothing else - just writing your fiction. Don’t include ‘checking emails’ or ‘answering letters’ or even ‘making notes’. Just the actual task of writing.
ii) Get everyone’s agreement. Easier said than done, but unless you do, your little timetable won’t be worth the screen it’s probably written on.
iii) Ideally, pick times that are interruption-free, or at least when you are less likely to be in demand. It’s possible to construct a schedule so that you are writing in the early hours of the morning - or even through the night, as long as you get sleep some other time- and to get a 300,000 word epic fantasy written in three months. I did it once, locking myself in an office and working between 2:00 am and 7:00 am and going home as the sun rose. But that’s an extreme. One long evening each week, or a weekend afternoon, or something like that, and, if you stick to it, you’ll find that in a few weeks you have made significant progress - provided you also apply the rest of the advice in this section and don’t keep interrupting yourself.
Fundamentally, though, you have to concentrate on stopping yourself doing something: you have to stop interrupting yourself.