A must is perfect coordination between the judiciary power and the police forces.
(Giving a search warrant on time, for instance)
Also, among police forces, perfect communication. Too often, we see (even here) a police chief not wanting to share info because he wants to get all the fame from catching the number one public enemy. Force is something to be used at the last moment (either when an attack is imminent and there is no other choice, or when all (or most of) the suspected people are gathered together in a single place. Force, then, must be very discreet and extremely selective (not killing important information sources or destroying things that might be very useful to track the others).The GIGN comes to mind! But before that, there's listening, following, infiltrating those groups.
And another thing: the best Islamist infiltrators will have to be muslims themselves, who even come from the same country as the terrorists.
We cannot rush blindly into their nest and provoke hatred when the population didn't hate us, as they themselves are the first victims of islamism.
Algeria is a good example (islamists killing algerians) and a reason why I find the "Islam is love" title completely inappropriate.

Raoul