Caster spells

For casters, the available spells vary a lot by guild - you will want to read their descriptions to determine what is important. This list points out some common useful spells, which may or may not be available at your guild. This is NOT a full list, several groups of important spells (such as the field spells) are not listed at all. But it should be enough to get you started.

Primary blast(s)

As with melee attacks, this is different in each caster guild, but should be studied as a priority, along with the cast X skills.

Protective spells

These differ a lot between guilds - Force absorption is the basic one, but there are many more. If your guild offers one, you probably want to have it.

Travel spells - Teleport without error, Summon, Relocate, Dimension door, Go, etc

Teleportation spells are very useful for obvious reasons. Most caster guilds offer one of two of these, and everyone except nomads can join the Navigator guild to get them all. Navigators are a 5-level guild, but even 2 or 3 levels are very useful to have.

Heal self

Basic healing spell, nothing surprising there. Mage guilds get this.

Cure light/serious/critical wounds, ...

Healing spells that work on others - several backgrounds and guilds offer the basic ones, tarmas get the better ones (minor/major heal, party heals) as well.

Floating disc

Very useful utility spell, lets you carry a lot of loot. Training it higher improves duration.

Identify

The usage is obvious - note that the spell is rather inaccurate. Folklorists and merchants get more information.

Invisibility

Very useful spell for exploring areas. Note that some monsters can see through it.

Infravision

See in darkness. Very important if your race doesn't have it. Later on, you can also get it as a permanent ability.

Water walking, Floating

These let you cross water and some other hazzards. Important if your race cannot swim/fly.

Light, Darkness

Spells that affect illumination around you. Useful if you don't have infravision, or if someone in your party has a race that requires darkness.