I was wondering about what tactics/strategies everyone uses during BG. It's always interesting to learn what others are doing and go, "hey, why didn't I think of that?"
For me, I have a few key strategies I use against enemies.
Archers - my party has four archers, so when I see enemies I just start blasting away until they reach my front line. I try to have my two tanks fight with melee weapons while my elf fighter and thief continue to blast away with arrows. This is probably a common strategy among gamers.
Choke Points - These are great. Find a narrow area where there is only room for one or two of your PCs (doorways are great for this, or outside natural narrow places). Have them block here, keeping the rest of the party safely behind them. This way, your two front liners only have to fight one or two creatures at a time. This works well when you have a large mob coming after you. While the foes are blocked battling your tanks, your archers or other PCs with missile weapons can blast away, while the front liners take care of the rest.
Flanking - I like to engage a foe with one character, then flank with the others. I will have another PC come up behind the foe, and if there are any more available PCs, they will flank from the sides. I don't think this gives any bonuses, but I have noticed that the foe usually stays focused on his first PC, so the others on the sides and/or back can chop away with impunity.
Doors - I have used this trick in BG1, BG2, and Icewind Dale, so I can't recall if it works in BG1. When faced with many enemies, I will have all my PCs wait in a room, while one PC stands off to the side right near the door. If you time it right, and the monsters are spread out a little, you can let a few of them in and then have your PC shut the door, thus blocking all the other monsters. They are unable to open doors. I think Siege of Dragonspear changed this though, because I tried this on that game and the monsters just opened the doors up.
With this tactic, you can take on the foes a few at a time instead of all at once.
Magic - Grease, grease, grease. This spell is so underrated! I love to use this to keep enemies at bay so I can pepper them with missile weapons while they plod along. Grease combined with Stinking Cloud and Web will usually render most if not all the foes incapacitated. Then a nice Fireball or two mops up the resistance. Bless and Doom are also good buffs. Animate Dead and the Monster Summoning spells come in handy when you need a little more muscle.
Withdrawing - This is probably a no brainer, but if my party is in a bad spot, I will have them retreat. I use Boots of Speed on all my PCs, so they can usually outrun their foes. This helps them reposition themselves, get healing, or use missile weapons.
Fighting spellcasters - This is probably a no-brainer, but I pick out spellcasters right away and start blasting them with missile weapons or spells to disrupt their casting. My cleric will use Hold Person and Silence 15' Radius to try to immobilize the spellcasters. Sometimes a straightforward charge works wonders as well. The spellcaster may get a spell or two off, but then has to contend with some beefy tanks right in his or her face.
Spread out - This works well when you are facing an enemy spellcaster. Have your characters spread out as far as they can, so they won't all get nailed by an area effect or a fireball.
Scouting - I usually send my thief and one of my tanks to scout ahead, the thief using his Find Traps ability. This way if you run into something, you will have an idea of what you're facing without your entire party blundering into some huge fight. The scouts can race back to the party and you'll have a little extra time to prepare.
Taking out missile weapons - When faced with foes where some have melee and some have missile weapons, take out the ones with missile weapons first. Otherwise while you're in melee, you're getting blasted with arrows or whatnot.
Some of these might be "duh!" tactics, but I just wanted to share my tactics and see what others are doing!