Jandrall Note:

Basically focus on the primary skills (Wizardry, Divinity, Psionic, Alchemy) and next to ignore the Realms (Fire, Water and so on...)
Instead raise the realms by training and using all different realms the whole time (in combat, buffing, before camp etc.) It doesnt matter if you fizzle the spell, you can gain skill in it anyway.
Constantly cast nonlethal spells at highest level possible...it wont harm you. Ofcourse some spells cant be stacked so you have to wait a while between.

Save your Spell choises at level up to be able to use more of the highlevel Spells when you get to them, its not necessary to have all low level spells. Spells up to level 4 can be bought and learned from books (even above lvl 4 but more rare). The books are expensive but can be pickpocketed if you like.

Good passive practise spells ( and very useful ) with level:
Air: Missile Shield 2
Fire: Light 1 (this you find very soon in game)
Water: Stamina 1
Earth: Armorplate 3
Divine: Enchanted Blade 1, Bless 1 and (ofcourse) Heal Wounds 1
Mental: Charm 1(when NPC near) or Detect Secrets 2

Good offensive practise spells with level:
Air: Sleep 1
Fire: Fireball 3
Water: Freeze Flesh 3 (hasnt got any good earlier ones)
Earth: Web 2
Divine: Magic Missile 2
Mental: Mindstab 1

Magic classes breakdown:

TennesseeErnieFord

Healers:
Alchemists- Heal (no heal alls); Cures (except for sane)
Priests- Heal all; Cures
Psionics- Heal HPs only; cure sane only

Attackers:
Alchemists- 13: 8 direct, 5 persist; 1 all
Mages- 15: 11 attack, 4 persist; 4 all
Priests- 8: 8 attack (no persist); 3 all
Psionics- 11: 6 attack, 5 persist; 3 all

Diminish Enemy:
Alchemists- 6
Mages- 10
Priests- 5
Psionics- 12

Specials (All have portal)
Alchemists- 3 (Chameleon, Knock, Light)
Mages- 8 (Enchant Blade/Miss. Shield, Secrets/X-Ray, Knock, Light, Curse, Shadow Hound, XRay)
Priests- 7 (Charm, Traps, ID, Light, Curse, Magic Shield, Armorplate)
Psionics- 6 (Chameleon, Charm, Secrets, Traps, ID, Mindread)

Key Features
Alchemists- voiceless spells, mix potions; good persist, good attacks; excellent diminish
Mages- resistances; most attack, most attack all; best boosters
Priests- pray, dispel; heal all, heal well; boosters
Psionics- mental resist; most persist spells, most diminish

Key Weakness
Alchemists- no heal all; best attacks later
Mages- vulnerable (HPs, voice)
Priests- no persist attacks; hurt all come late
Psionics- voice, lots of resistant creatures

Key Realms
Alchemists- Air=best (); no mental;
Mages- All Realms have good spells; `
Priests- Divine=best; weak fire (Light/Ltng only); Water (Paralyze, Rest)
Psionics- Mental=best; no mental; excellent fire

Klef

I want to know one thing. My bishop has all skills doing fine, but Divinity stop growing since level.3,4 maybe. While Skills like Wizardry and Alchemist grow up while using spells, divinity seems to not grow. How can i grow it?

Zurai

Bishops gain points in the highest school that the spell they cast resides in. If wizardry/ Alchemy/Psionics are higher than Divinity, then those will raise instead of divinity. Cast spells that only reside in the Divinity school, or only reside in Divinity and schools with fewer points, and your Divinity will increase.