this post is not mine, but I remember it from the depths of newgroups in the 90's, so posting it here for posterity.
Well, since no dungeon exists in a vaccum: "research, research, research" becomes the mantra of the time. Locals always seem to have "legends of the dark times" when the place was active. Use your time wisely and spread a bit of the kings gold around among the tavern flies and they'll likely put you on to someone who knows something valuable to your survival.
Next, always be flexible. Don't EVER depend on any single tactic (other than advanced research, perhaps) to carry you through. What a man can devise as a stop gap measure another man can think of a way to neutralize or turn into a trap trigger in and of itself.
Carrying boat loads of flammable oil, for instance, is damned likely to turn the carrier into a short lived Richard Pryor impersonator in some cases, so be prepared.
One thing that doesn't hurt is: light crossbows... even thrown weapons and shortbows are stupidly hard to use indoors beyond a hand full of feet, while the flat trajectory of a light crossbow makes it optimal... and a simple -2 non proficiency penalty (the absolute worst this should ever be since these are the closest thing to an idiot proof medieval weapon) if no has proficiency with one is hardly a big deal to most fighters.
All the emergence supplies... such as light rope and spikes and poles that can be carried, with NO ENCUMBRANCE, can be life savers, so make sure someone is toting them.
An obvious one if you have a mixed racial party is keeping the shorter members to the front and the taller to the back with those crossbows to fire over their heads if that scenario can be done (ie: dwarves and halflings and gnomes up front in normal march order). The front people, if they aren't warriors, can always fall back, but that initial volley of bolts doesn't need to suffer extra penalties because you have to shoot around the big, plate armoured warrior always wants to be out front.
Keeping in mind the strengths of the various members is also a neccesity. It can be FAR more efficient and safe to have a dwarven thief who's a "traps man" up front than a defacto stealthier halfling fighter if you hit a section with alot of traps. Stay flexible and stay safe.