As Mr. King says, the most important thing in life, especially in the arts, is sitting down and doing the work, regardless of whether or not you feel inspired. At least if you have any interest in doing this sort of work full time (or even as a serious part-time endeavor).
I know personally that I’ve often had issues with maintaining focus. When you’re working for yourself it can be difficult to stay on task, even when you want to do something. But one of the methods I’ve found that has worked for me is the Pomodoro Technique.
For those who are unfamiliar, the basic concept is that you set a timer for 25 minutes and focus intensely on whatever you’re doing for that time. Following that, you take a 5 minute break and then get back to another session. You can line up however many sessions you’d like, but I recommend doing three or four in a row and then taking a longer break after that.
You can set the timer for any time that you’d like, but I would highly recommend sticking to 25 minutes if you’ve been having trouble focusing. Personally I’ve found the shorter time frame helps a lot. Thinking that you’re going to commit to a longer period of time without any type of break can be daunting, but 25 minutes worth of focus is very doable, especially if you’re just starting out with this technique.
Now, for writing, you’ll probably want to track your word count as well. For 25 minutes worth of writing, I would say that 500 words is a good target to reach (which is about 1.5 pages double spaced). Again, if you’re just starting to do work with this technique, then don’t beat yourself up if you fall short of this, but I think 500 words is a good benchmark to go for per session.
This is one of the better productivity techniques that I’ve tried, so if you’re struggling with getting writing done, I definitely recommend trying this method.