At the source, the states promoting and funding it need to be cut off from access to the internatonal stage, and how we choose who they are should be on facts not personal agendas and profits, even if they are alllies.
Education and inclusion we need to teach tollerance and mutual respect, all faith shools should be banned in fact I would advocate a ban on religious teaching in schools unless it is on a multifaith basis where you learn about the lot.
Anyone found to be preaching hate and division should be arrested, charged and tried, if found guilty a minimum sentance applied.
Dom't interfere unless absolutely necessary (mass genocide for example) in other countries disputes, unless we have a cohesive plan for the aftermath. And don't do this by arming a number of factions without a due diligence, so it doesn't bite us on the arse later. (syrian anti-government groups sell ammunitions we supply to isis regulary unofficially)
As a last resort when necessary lethal force.