I think the "warm-up" principle for any activity is important. You wouldn't run a marathon or perform an arabesque in Swan Lake without stretching your muscles first, would you? So why would you sit down at the computer to write a story without getting your brain and finger tips ready for some serious writing?
For writing sessions out of the house, I usually pack a copy of Elizabeth Berg's book, Escaping into the Open: the Art of Writing True, whatever current novel I am reading, a blank journal and my laptop. That's a lot of gear! I start by reading someone else's good writing for inspiration. I often think that maybe by osmosis, talent will seep into my pores. A good read should be accompanied by a nice steaming cup of something delightfully aromatic and flavorful, whether for you that means a cup of Earl Grey tea or an indulgent Cinnamon Dolce Latte. My next step is to dip into Elizabeth Berg's book on writing in which she has wonderful writing exercises to get you going. It doesn't have to be a thesis. Even a paragraph or two in which you practice your descriptive language or dialogue can be helpful. That just leaves your empty notebook or computer screen to be filled. It depends on the day, but I am usually old-fashioned about writing things in long hand first, and then typing it up during the editing stage. There is something about scratching things out, writing little notes to yourself in the margins, perhaps doodles, that appeals to me. Also it doesn't hurt to have a beautiful pen to write with for inspiration. For Valentine's Day my husband gave me a gorgeous, purple "True Writer" pen from Levenger. I'm not trying to plug www.Levenger.com here, but I am addicted to all of their elegant paper and pen goods!
Given the fact that I only book about 2 hours of writing time, so that I can get back to my little boys and relieve Daddy, these steps can take as little or as much time as you have. If you feel you need practice, then just work on the writing exercises. Whatever suits you is best. There is no right way to write after all. I am just sharing one of my routines for getting inside of what Natalie Goldberg refers to as the "wild mind" of the writer. So - read, brainstorm, write, edit, write some more (look out the window at spring blooms, because life is too short) ... and remember to enjoy that coffee house java!