People often ask me how I write so many books. The answer to that question is... I write. I, like so many writers, go through cycle where I could sit down to my computer and no matter how many characters are in my brain, I could not write a scene if I tried.
But then there are those other times. Those times when the muse strikes me full force. I think it is so important to capture these moments and write as much as you possibly can. Writing, like any other pursuit in your life, should be taken seriously. It does not always demand your time, but when it does, answer the call. Think of it like your children. Most of the time they can go to school and come home and the routine is a normal pace. Sometimes, though, they can get sick at school and require you to take time off your job for come home, do hospital, and give a little bit of parental loving.
This is not to say that I am suggesting you take time away from your regular job, this is just to say that if you really take your writing seriously, you will make sure to make time for your muse. She can be your best friend, or your worst enemy, depending on how much attention you give her.