Perhaps the following is the answer:
More armed police on the streets,
Tighter security at public venues, border controls, etc.,
Arrest more people who are on the 'watch list' - e.g. FB comments calling for violent campaigns to introduce Sharia law should be regarded as an arrestable offence (treason) that has a long custodial sentence,
Stop fighters and their families returning from ISIS and areas controlled by other terrorists,
Get mosques to sign up to anti-terrorist measures (those that refuse should have their charity status revoked and should be denied government funding),
Step up the bombing campaign against terrorist groups abroad (bomb the bastards).