Besides the tips above, there are some basic things that can help even while your character is at a low level.
First, although some would consider it a cheat, one of your greatest advantages is you can see the future (sort of). So you see the red dots on the map along the road you want to explore. Do a save and walk right up until you trigger a fight. Don't worry about fighting so much as who your enemy is, how are they positioned, and how they fight. Now reload and think how can I beat these guys, now that I know who they are, where they are, what spells they cast, etc. Whom do I need to take out first? (usually a mage hiding in the background)
If you can locate a choke point where a passage narrows near the battle ground, maybe send a hasted summoned creature to the battle ground to initiate the fight. Then have him run back through the choke point toward the party-- who is all buffed up, waiting in ambush. If you have characters that can cast an oil slick and summon a fire elemental, once the elemental is heading toward the battle ground to initiate the fight, cast an oil slick at the choke point. As the elemental races back to the party, he will set the oil slick on fire as he passes though it.
This and the many examples posted above give you some idea of the kinds of things you can do the even the odds somewhat. Although I wish that all the fight weren't like this, they are in this game, so find the joy in figuring out your way of beating the odds. Good luck--you'll need it!
