flameblast+what support gems?

so im using flameblast build i very like it but i have no idea wich support gems i should use together with flameblast all i was using was casting speed i dont know anything else wich support gems would be very good with flameblast any ideas?

Fire penetration is a must. Spell Echo, Increased AoE, Concentrated Effect, Chance to Ignite, Elemental Proliferation, Increased Critical Strikes, Increased Critical Damage, Power Charge on Crit, increased Burning Damage, and Culling Strike all work with it. Depends on your build really. With quality Flameblast you don't need to crit to ignite. Using the Chance to ignite gem with a 20 quality Flameblast will pretty much always ignite, so Elemental Proliferation would be good if you aren't killing on the initial hit.