General:

Be very careful about spending skill points unless you're ok spending money to respec, make sure the skill you are investing in will even work. Many cases it will do next to nothing, even if it seems obvious that it's good. Double check with others

Skills that are calculated based on a stat (str/agil) increase every 10 of that stat. So having 70 str is several % better than 69 str with 1-3 extra skill points in use.

Mages:

prioritize primary elemental dmg, class skill, shadow resist, res mastery. defence(?) in roughly that order.

Resist priority:

shadow (pixes/mages do shadow dmg mostly)

energy(?) warlock beams are shadow, are enemy mages energy if they're wizards?

Warlocks:

Shadow dmg->shadow power->shadow resist->few in energy res->res mastery->Defence

Leech seems like it kinda sucks, with it's cooldown you can't count on it reliably.

Melee:

prioritize class skill(s), do not put skills in weapon types if theres a skill that uses it instead. 'Spin' or 'multi shot' doesn't use your 'sword/2h/bow' skill points for example.

Warrior:

Paladin:

inner str->critical hit->armor->def tactics->shield->shield mastery->2h (used for pvp/hitting bosses in back)

armor spell increase is likely especially good for pally, since it has 4 diff armor spells, most classes have just 2.

stats: