Air combo - for air juggling in 1vs1 PVP
Meteor fall - launcher for air combo, could also cancel some attacks, useful for PVP
Focus/slow heal - I don't think I should explain why, pretty obvious, but you might want to deduct points from focus cause it's not THAT useful, though only do it if you REALLY need points
Diffusion cannon - prerequisite for lightning strike
Lightning strike - same as meteor fall
Rain of fire - high DPS
Casting acceleration - IMBA for myrms. Required for fast casting of spark rock (too slow otherwise). Reason why it's imba for myrms - instant stumble
Detection - level 5 is a must IMO for high level mobs (after all, +15 zauharant weapon only deals ~3K*2 with double shot on level 70+ mobs @ drakos). A must for high level PVE, also a very nice addition for PVP, especially against magicians.
Barbarian - catcher for PVP
Witch's curse - will be nerfed, can manage without anyway
MP recovery increase, wide heal, sanctuary, instant heal, resurrection - no explanation needed
Staff mastery - IMO 50 skill points for 35% extra base matk = OK, so either 1 (as prerequisite) or 5 if you have enough spare points
Striking - level 5 is a must, 500atk/matk for 3 minutes is a decent boost, one of the best buffs.
Blessing - 0 because it's useless.
Chain lightning - 0 also because X spamming, spark rock AND rain of fire = faster DPS, making this buggy skill completely useless (perhaps not for PVP, but I wouldn't get it anyway)
Spark rock - pro skill, enough said
Cure - level 5 for low CD and more debuffs curing.
HP restore/barrier/energy absorption/perfect seal - decent skills, but not decent enough to use important skill points on.
Quagmire & muddy mud - helps in mass PVP
Double shot - ????????
Healing wave - crappy skill, not worth the skill points at all
Blood fever - same as ^
Awakening - prerequisite... I think?
Lightning storm - useless skill, only somewhat good in PVE against a large group of mobs. Causes FPS lags to everyone around you. Might bug your character so that you can't hit/use skills until map change.
Lightning rod - level 5 for much wider range, a must for mass PVP
Wrath of heaven - could use level 1, but level 5 = awesome damage, hits 4 times, stuns for longer.
Could use the following combo:
Freeze->WoH->spark rock->rain of fire (and a bit of x spamming if you're into it)->freeze->WoH (level 5 should have low enough CD to use it again)->rain of fire->freeze->x spam (if you're into it).