As I mentioned below, the "What would ISIS not want us to do?" is not a good heuristic, because by asking it you implicitly accept their world view.
I think part of the problem here is that it is difficult to discern how rational ISIS is as an organization. It is some combination of militia group; millennialist cult; and breakaway state. (It's interesting that it has changed its name a couple times.) As best I can tell, the overall game plan of ISIS is -- generally speaking -- to follow in the footsteps of the most fundamental religious doctrine it can, and have faith that this will result in their eventual success. Under such circumstances, I don't think it's very useful to "avoid playing into ISIS's hands."
This may be a more useful consideration if the enemy was some kind of James Bond super-villain who was carefully scheming at every stage. Even then, you never know if the other fellow really wants something or if he is only pretending to as some kind of ruse or feint.
The problem is that their game plan is likely to be something more or less along the lines of, "Start a war between Islam and the rest of the world. Since our religion basically teaches that we are inevitably going to conquer the world by force, we will be guaranteed victory in such a war."
The religion is false, so they would not win such a war. But it would be an extremely bad thing if it happened at all, regardless of whether they win. So playing into their hands is probably not a good idea anyway, even though they are wrong.
Here's my op-ed that uses long-term orientation, probabilistic thinking, numeracy, consider the alternative, reaching our actual goals, avoiding intuitive emotional reactions and attention bias, and other rationality techniques to suggest more rational responses to the Paris attacks and the ISIS threat. It's published in the Sunday edition of The Plain Dealer, a major newspaper (16th in the US). This is part of my broader project, Intentional Insights, of conveying rational thinking, including about politics, to a broad audience to raise the sanity waterline.