And turn on most of the autopauses, too, unless you really want to be playing an rts type game.

Don't forget to up your defenses too. resisting attacks helps a lot!

Yep. When you unlock fourth level cleric spells*, Protection from Evil 10' radius can effectively give everyone in your party +2 AC and a +2 bonus to all saves, since (apparently) all the normal enemies in BG are considered evil. The duration's long enough that it'll probably be most of the day, especially at high levels. Highly recommended to have active at all times.

*Note I specifically say 'cleric': druids don't get this spell.

Also get the spell that prevents Fear. >.> It will help a lot early on.

Good point - that also lasts long enough to have on all the time (I think - check the description).

The Cleric spell "Remove Fear" also works to prevent fear, so you can use that instead of using up an offensive Mage spell-slot.

Remove fear is quick to cast, so you can often simply cast it when someone gets affected by fear, especially if the caster with the spell tends to be out of range of AoE spells. In BG2, I have it prepared on a cleric/mage multiclass, and can cast it on those odd occasions it's needed.

Incidentally, there's no way of casting a lower level spell in a higher level slot, is there? Other than contingency, wondrous recall, etc, which only work for specific level slots. There aren't any proper healing spells in the second tier, other than goodberry, and I have liked to fill them with Cure Light Wounds.

I generally use potions during fights, if I need to heal. There are also high level spells (Regeneration) which you can cast before the battle.

Casting speed is dependent on many things. Stats, equipment, etc. A Cleric does have a slow casting time normally, but they are allowed an Insta-Cast Cure spell at any level(I believe. Might be IWD I be thinking of)

No, each spell has a casting time that you can see in the description. A spell that is described as instantanious or casting time 1 cannot be interrupted. A spell with casting time 9 needs an entire round to be cast. If you take any damage during casting or you you get a status effect that prevents you from casting or you move, than the spell is lost. This is independent of your class (mage or cleric).

The abilities you get during the story have the same effect as a spell (such es cure minor wounds) but they are instantanious (unlike the spell they "copy" which has a casting time).

Edit: In the DnD3 system (neverwinter nights 1+2 for sure, have not played IWD2 or TOEE yet) clerics can convert every spell they know in a cure (or inflict if evil) spell of the same level. This is not the case in DnD2 like the baldurs gate series.

Certain NPCs have special abilities similar to those gained by 'you' during the game. For instance, Dynaheir has several uses per day of slow poison, which can be very useful and saves you spellslots. As a general rule, these special abilities take no time to cast (and can be found by clicking on the star to the far right of the person's options for activities: don't forget to do that with new party members/after the various dreams you have, to see if there's anything new there).

It's also possible to gain items, especially in BG2, which speed up your casting time. That can be very useful in getting a slow cast spell off without it being interrupted.

I think in ToB you can learn a spell ("improved alancrity" I guess) That allows you to cast a new spell once your old spell is finished. You do not have to wait until the end of the round. And there are also items that reduce your casting time a lot ("robe of vecna" I guess). Both things together make your mage an insane magic machine gun.

Its been a while since I played bg so I am not sure about the names.

See thought I had the wrong game. But I was never too fond of Clerics anyway. I always used potions, and the Druid I think I tried playing as a cleric, and didn't like it. But anywho, I use Scrolls and Potions a lot of the time.