A good strategy against a lot of enemies to just wait for them to approach you and then stab away, back up, and then stab away again. Rinse and repeat until they die. This will save you some HP in the long run.
Use magic sparingly. Using magic to attack most enemies is useless in my opinion since you can just hack them with your weapons. It's better to use it for curing. Goldmoon and Raistlin are the only two characters that can use magic but the have a limited amount of it.
Search everywhere for items. A lot of them are hidden away in some obscure room but most of them are useful.
Use rest when you can. It will heal your party and allow you to save your magic and curing items for something more critical.
Use Tanis, Caramon, Strum, and Riverwind for physical attacking. Raistlin and Goldmoon should only be used for their magic, curative or attacking, it doesn't matter. Tasselhoff and Flint can be used for ranged attacks but otherwise they're backup if the others are weak.
When you use projectile spells, face in the direction you want it to go before you use it. Otherwise, you've just wasted MP.
Don't let your party members die if you can help it. That probably sounds obvious, but it's much cheaper to heal them than to revive them.