Well this is a huge area to cover but here's some
Name (level I suggest for the skill)
-Ball lightning (1/3) Some like to level. I don't think it's worth it
-Heal (5) A must have
-Earth protection (1/3/5) With 50% def at level 5 maybe I should level it? Haven't yet though
-Blind (3/5) Blind good in pvp and arena
-Quake (1/3/5) Quake quite buggy but also works in farm as well as arena
-Shield (1/3) Good damage, not necessary
-Totem (1/3) Good damage, not necessary
-Ancestors hand (1) lvl1 does perfectly fine
-Tribe's ritual (don't know) Maybe it's good in 2v2 arena with a lock?
-Energy field (1/maybe 3 don't really know) Most chars should have a good enough energy regen by level 18?
These are my thoughts