Priest and druid spells partially overlap: Druids can cast all the following spells, while clerics can cast only those not marked "druid only."
Type: Defense
Strategy: Absorbing a portion of all damage done to the caster and increasing with the level of the caster, this spell is a great, basic armor spell. Though it will taper off, it is useful and stays so. Cast it before any major battle.
Importance: High
Type: Imbuement
Strategy: Affecting all creatures in a certain area with bonus to luck and dice rolls, bless is another acceptable buff-up spell. The dice rolls will make a small difference in your combat abilities, and it's worth casting if you have the time before major battles.
Importance: Moderate
Type: Hindrance
Strategy: This spell renders a creature unconscious for one round. The spell, with no saving throw, gives you one free round to do as you will before the creature returns to normal. A lot can happen in one round.
Importance: High
Type: Heal
Strategy: Cast this spell on a hurt party member. It heals one to eight points of damage. For Baldur's Gate II, that amount is negligible. However, it is useful to cut down on the number of hours spent resting, so if you find no other worthwhile spells, fill level 1 up with this.
Importance: Low
Type: Detection
Strategy: Use this spell to find which creatures are evil in the area. When cast, a list will be made of all evil creatures. It's useful if you missed any enemies in a dungeon, and it's useful to determine motives and alignment.
Importance: Moderate
Type: Hindrance
Strategy: Giving a +2 THACO to the target, this spell actually manages to lower the target's combat abilities a noticeably small amount. The -2 to all general rolls, however, will help with spells cast in the future on the target as well as your ability to hit the target. In general, it's a nifty, if small, spell.
Importance: Moderate
Type: Hindrance - druid only
Strategy: This is another great spell to keep the masses off of you while you fight just a few enemies at a time. Entangle will create a large area of effect that will stop enemies from moving unless they make a save at +2. This is a spell to have in your memory as you go into almost any battle, but beware - you can get your own party stuck, too. So, this is another one of those spells to cast at a distance, unless you want to take the risk.
Importance: Moderate
Type: Missile damage
Strategy: A great principal level 1 damage spell, magical stone creates a projectile that does one to four points of damage to the target. The one to four points of damage is irresistible and quite good for a level 1 spell. Obviously, one to four points of damage is not great, but at level 1, it is nice for a small punch.
Importance: Moderate
Type: Defense
Strategy: This spell will become increasingly more useful as the game progresses. Not only is it a must for summoning minions, it will also protect you against many demons found in the later parts of the game. One particular battle comes to mind where there are hordes of demons, and casting this spell will let you turn the tide of battle from an impossible situation to an easy victory. However, if you happen to have a class like a paladin in your party, he will come with plenty of these spells as special abilities, so you shouldn't bother memorizing it.
Importance: High or low, depending on party makeup
Type: Cure, heal, and dispel
Strategy: If your party members are afflicted by natural or magically induced fear, this spell will cure them. Also, it will help them resist it for the duration of the spell. Since fear is a common effect of spells in Baldur's Gate II, remove fear is actually quite useful.
Importance: Moderate
Type: Defense
Strategy: When sanctuary is cast, the target can no longer take any offensive or defensive action without destroying the spell. A wonderful spell if you find your priest low in hit points, it will give him time to rest up, heal, and rejoin the battle without dying.
Importance: Moderate
Type: Summoning
Strategy: This spell summons a magical club for the caster. In Baldur's Gate II, you will have a better weapon than this will summon, so it is pointless and, actually, detrimental.
Importance: None