This is why I signed up for Beeminder.
I'm happy to share my experience so far in the hope that it's useful for someone with the same goal.
I used this quote from Neil Gaiman as my starting point
My priorities are to get words down on the page every day and to force myself to finish things (even if they're terrible!)
I think if I do that it will be hard not to get better quite quickly.
I'm using the Draftin integration to measure words written. It's a basic writing app that seems to get the job done and was easy to setup.
I only write short stories, poems and essays in Draftin and my rule is that I can work on a maximum of 3 pieces at a time.
If I want to start a new piece and include it in my word count I have to force myself to finish one of the others first.
I also attend a creative writing evening class where I read pieces out every few weeks, which provides some accountability to finish things too.
I started off with a goal of writing 50 words per day, thinking let's start with a stupidly easy goal to build the habit. That's gone up to 100 per day now.
I've been going about a month and haven't derailed so far. I've written 3500 words and finished 2 pieces (as very unpolished first drafts).
Although that sounds good (and it is a big improvement on what I wrote the month before: 0 words!) the biggest problem I'm facing is that I'm not writing very consistently.
Instead of writing 100 words each day I'm writing 300 one day then nothing for 3 days. Then 1000 and then nothing for a week. Again, it's better than not writing at all but it isn't the writing every day, or nearly every day, habit that I had in mind to begin with.
There is a feature called 'Automatically trim safety buffer' which would solve that, but it's only available on the paid Premium Plan.