Routines build habits. Habits can be very important to building foundations. Good habits anyway. But, and this is a big but, for me anyway, sometimes routines and habits need to be changed or adjusted to keep things fresh.
I've started going to the gym. This is my fourth week now that I've been going consistantly. And it feels GREAT! But, even in those four weeks, I've needed to mix-it-up a bit in the routine to keep things interesting. Like I create little challenges for myself in the number of calories I'll burn in a session, or I'll change my equipment routine or the time that I go. Keeping it interesting is just as important for results as the actual routine.
I bring this up, because I've found this also holds true for my writing. Routines are important to leading to good writing habits, BUT I've found that I need to mix-it-up sometimes to spark my creativity. Examples of how I do that? Instead of writing at night, maybe I'll get up early and write in the morning OR instead of writing at my desk, I'll take my laptop and write in the car outside a park on my lunch break. Sometimes I'll revise on the laptop, and others I'll print out a few pages and revise on paper. I'll write in silence, and sometimes I'll add some background music or a nature CD.
Keeping the routine interesting and fresh is the best way to ensure that you'll maintain the routine. At least, it has been for me.