Probably posting this too late to help op, but what the heck.
1. As others have said, you need to pause this game during the fights. I like to set AutoPause (a) enemy sighted; (

spell cast; © trap found; and (d) weapon unusable. That way, you have time to plan your reaction to enemies and chose your next spell attack in the middle of a fight. Trap found is to prevent your thief from accidentally killing him/herself while searching around, and weapon unusable is for when you run out of arrows.
2. When you start out, do use a 6 person party. Your goal should be to try to get 2 fighters, 2 arcane spellcasters (magi), 1 healer (cleric or druid) and 1 thief. The first NPCs you meet actually fit this pattern: Imoen (thief but can be dualed to a mage), Montaron (thief/fighter), Xzar (mage), Khalid (fighter) and Jahiera (fighter/druid). Just bear in mind that eventually you may want to (likely, have to) change a couple of these team members.
3. Thieves: spend all your points on Find Traps until you get it to near 100%, and then spend it all on Open Locks (the Knock spell can cover this gap until you get it up to 100%). You can round the skills out later. You need to get Find Traps up relatively early to move the story along. You can always come back and deal with the locked containers later. (If you have two thieves, I'd dedicate one to traps and the other to locks.) As for fighting, give your thieves Short Bows and kept them out of hand to hand combat range! (Pause the game and move them back if need be.)
4. Magi: as others have said, your goal should be to get Sleep. That will disable lots of low level enemy mobs. Ignore the damage spells (Magic Missiles) until you later in the game--their damage increases with level and generally start weak. For your second level spella, learn to use Web and Stinking Cloud properly. They are better disablers, but they are not party-friendly (by that, I mean if they hit your people, these spells can disable them too). The best way to use them if to have one person scout ahead and when they see the bad guys, retreat. This way, the spellcasfer now knows where to fire the Web/Cloud. Proper use of these disablers will make many sections of the game much easier. As for weapons, give them a sling. Darts fire faster, but slings have better range. And you want to keep your spellcasters out of hand to hand combat.
5. Mage Spells: not all BG1 spells are equals. Some are great. Others are basically useless. Test and find the ones you like. But consider Sleep and Magic Missile for level 1. Web/Cloud/Invisibility/Mirror Image for level 2. And Fireball/Haste/Slow for level 3.
6. Healers: as also noted above, don't horde potions. There are plenty to be found or bought. Plenty! But it also helps to have a cleric or druid. Cure Light Wounds is a good solid spell. But look at the other spells as well. Read the descriptions. Some spells protect against fear. Others against petrification. Others give you bonuses to AC and saving throws. Test them out. Experiment. But try to use the one that have the longest durations (btw, 1 turn = 10 rounds). Weapons again should be the sling first. Secondary weapons can be a club/mace/scimitar + a shield. Note that unlike magi, clerics/druids can wear (at least some) armor. So gear em up!
7. Fighters: try to put the best armor you can on them. If you have two, it is often a good idea to give one a shield and a single handed weapon, and to give the other a bow and a two-handed weapon. The first guy (best armored, lowest AC) is your tank. The second guy is your sniper. Move the first guy up to engage the enemy. Better yet, once the enemies lock on to him, have him run around in a big circle away from your team. That allows the rest of the team to shoot the enemy with missile weapons and spells. This can be a remarkably effective tactic if you get used to it. But having the best armor on your "rabbit" helps in case he gets caught... which can and does happen...
8. Hand to hand combat: avoid this whenever possible. Your characters in BG1 are easy to kill. A 3rd level fighter probably has only has around 25 hp (assuming avg die rolls). It is very possible for him to get killed in 1-2 rounds of hand to hand combat by even weak opponents if you get unlucky. So if you have to fight hand to hand, try to make sure that the person doing it has some healing potions, maybe a speed or strength or heroism potion, and use those freely.
9. Resting: don't do this in the wilderness if you are hurt/low on spells (which is most of the time you would want to rest anyway). Go back to town and stay at the inn for a gp or three. Your healer can get everyone back to fighting shape quick. And you can rest again to recharge his/her spells. BG1 is not on a timer so rest as often as you like!
These are just general ideas. Feel free to disregard them whenever is convenient.

Good luck!