One of our members has a really good one. She has chosen a day when she writes and this has become a great habit. If it's Saturday, she writes. Not sure what other people have set but setting aside a time when write is what you do and nothing else is a good habit to establish. How can you call yourself a writer if you don't write.
For me, I set a goal of 1000 words a day. Not all of this thousand is new words but much is. Now there are days when the words come easy and I will continue to work on that scene. I've done as many as four to five thousand words on a good day but that doesn't take away the goal for the next day. There are also days when life has interrupted and those thousand words are finished at midnith but they're done.
So my advice is if you want to be a writer, set yourself goals. Find a day or a time when no matter what you sit down and write. This will become a habit and you will feel the need to keep the habit. Set a goal of words. If you wrote just one page a day, think of how many pages you would have in 365 days. More than a book. Do the math. So my advice is to find a day or a time and a goal and you'll find you're not just calling yourself a writer. You will be one.