The title of this post is a question that Anthony and I, along with lots and lots and lots of other people, get asked occasionally. I'd be interested in how others answer it, but my answer is pretty firm. In general, you shouldn't be aiming for publication until after you've finished writing your PhD dissertation. The PhD is the single most important piece of writing for 99.9% of young scholars, and all efforts should be put into it. There will be the occasional exception where someone is able to publish something prior, but those should remain exceptions. I understand all too well the desire to have some publications on your CV straight out of the gate in order to compete in a historically insane job market. But, to the best of one's abilities, he or she should resist that pressure and try to focus on the PhD. Has anyone else given or received helpful advice on this topic?
UPDATE: In light of some discussion on Facebook, I probably need to clarify my point. It's not that publishing before the PhD is necessarily bad; it's that trying to publish at the expense of the PhD is. If someone can publish articles en route, and it doesn't result in them neglecting their doctoral work, that's great and will only help them on the job market. But those publications should spring from work related to the doctorate. I think that neglecting one's doctoral work in order to pursue writing unrelated journal articles, etc., is a bad idea. There's no doubt some regionalism at work here as well, as I did my PhD, and now currently teach, in the British system. In the US system, seminar papers can often easily lead to publishable articles prior even to commencing doctoral work.