One question I sometimes have to answer before I write is one about whose story it actually is that I'm about to tell. There are times of course where this question doesn't come up. Sometimes it's obvious to me from the first spark of the idea who is going to tell the story. But other times, when I have an idea for a great story instead of a character, I have to figure out who is going to be telling that story.
This is another one of those pesky writing puzzles that has an impact on so many aspects of the story. WHO tells the story leads to questions of whether the story should be told in first person or third person, past tense or present tense, intimate or observatory, etc. etc. As with any choice you make, there are benefits and pitfalls to each option. I think one of the keys to successfully writing (and completing) a story is knowing the answers to these questions before hand. A little time spent thinking through these options before setting out to write can save the writer a ton of frustration throughout the process.
I'm currently going through this process with two story ideas of mine. At times it can be like riding a never-ending roller coaster where each turn winds its way back to a past loop. But that's okay. In my opinion, it is in these stages where the writer really gets to enjoy his or her story and have fun with it.
As with editing, I believe most young writers don't realize that thinking is another huge part of the writing process. The actual writing is just one step. To be able to present the story you set out to tell, you must be able to shape your writing by knowing how to manipulate it.