First, stop any more potential terrorists coming in I.E. get out of the EU.
1a) Secure our borders at all costs.
Second, reintroduce identity cards on a temporary basis (as happened in WW2). I object to this in general terms, but accept the current need.
Third, Islamic terrorism comes from Muslims alone, so all Muslims need to be registered - sorry, but that is how it is - and mosques need to be either closed or monitored closely with CCTV etc..
There are other, minor points, but these seem to me to be a basic need. Otherwise we shall have to populate entire islands with Muslims internees (as happened in WW2 to Germans sent to the I.o.M.).