In my recent advice column to newbie journalists, I suggested writing each story three times, three different ways. And I stick by that! It’s not okay to reuse quotes without acknowledging that they’ve already been published or without linking to the previously published piece. It is, however, completely fair to mine the same subject matter and find a new angle or thesis on the topic and to pitch a new (but related) piece to another publication. I also think it’s fine to use portions of an interview conducted for one outlet in a piece for a different outlet—as long as the original outlet is mentioned, along with the date and original context of the interview.
A good rule of thumb? Quote your own previously published work as if you’re quoting another journalist, and you’ll stay in the clear. And if you have any doubts at all, raise them with your editor. If she thinks you’re crossing a line, believe me, she’ll let you know.