, you can automate the process entirely using specialized blocks: MFR Mob Grinder MineFactory Reloaded
Because water doesn't work in the Nether, you must use lava flows or a mechanical funnel (pistons and pressure plates) to push Blazes into a central drop. minecraft 1.7.10 xp farm
~30 levels in 10 minutes. This is slow, but safe. , you can automate the process entirely using