I switch between stories. A lot. But one rule I've found that helps minimize the never-get-it-done part is that a story has not lost all interest just because I sit down and have no interest in it. I have to actually take a stab at it and get nowhere, slowly, before I switch.
And when a story feels flat, stale, and profitable, while I'm writing it, the proper thing is to loop back around to other stories in half-done states, whether needing the first draft done or revision. And they often don't look interesting at first glance. Getting some ink on the paper (or photons on the screen) is necessary to evaluate whether it's really dormant.
As a general rule. When something jells about a story on the backburner, sometimes I'm unable to resist the impulse to pull it off and work on it. But things get done that way, so it's not that bad. 0:)