One thing I've learned over the past month or so is that you should never write for the sake of writing--certainly, art for art's sake is the purest form of masturbation that doesn't require a lubricant.
I tried writing a play with a friend a couple weeks back. We sat down and we plotted it out. We sketched sets and blocking. We had some great ideas for the stage and the structure--but no story to fill the scaffolding in with. See, we came to the canvas (or whiteboard, in our case) with no plan. No core idea. No driving principle on which we would forge our art. In truth, I haven't really ever had any ideas that would best suit the theatre, and thus I have not written any plays of late. I am strongest as a prose writer, I think, or at least that's the way I best know how to articulate myself.
And so the play is not going ahead, as of right now. Maybe if there's a story either or both of us wish to explore in ernest, we will pick up our set of ideas again. There were some beautiful concepts, some wonderful physical ideas that just were so empty because they served no master--they served no conviction.
I believe you cannot just sit down and say 'I am going to write a story' and expect it to be very good. I would know--I did it for years. I think you have to sit down with a problem, or a feeling, or something you're desperate to explore, and start there. Start at the core, and build the art around it. Not the other way around.