[mlangsdorf]

Things I've learned from 5 years of playing and running DF:
* Ambushes are deadly. A bunch of mook monsters with crossbows who can take aimed shots at the PCs from behind can be a TPK. Be very careful with hidden/invisible monsters if your PCs don't have countermeasures.
* Use low-sanctity and low- or no mana zones liberally. Wizards are balanced on the implicit assumption that their toys aren't going to work all the time. They should run into that problem at least once every adventure. Same with clerics.
* Anything that needs to be secure needs to be protected against magic: made of meteoric iron, in a no-mana zone, protected by Mage Lock and various warding spells, whatever.
* If you have a flying PC, read the rules on flight vary carefully. An SM0 delver with Winged Flight needs at least 6' of clearance on each side, to the back, and over the head in order to fly. Flight should be useful but it shouldn't be always available. Wizards using Flight to scout should remember that you can't see mana zone boundaries in advance, and they are liable to drop out of the sky at any time.
* Spellcasters get less abusive if there's a time limit and they can't futz around, casting spells all the time and recovering. Up the difficulty of the out-of-combat challenges if there's plenty of time.
* You'll need to revise a lot of spells, more or less as needed, to deal with the PCs. Problematic spells include but are by no means limited to Shape Earth, Alter Terrain, Hang, Delay, Reflex, and Bless.
* Most delvers have no good way to deal with diffuse foes, so don't overuse them. On the other hand, they're a good challenge, so don't avoid them either.
* If you have an Elven Scout (you probably will), make sure that he understands how you're interpreting Sense of Duty (Nature).
* Any monster that attacks with an unarmored limb is pretty much not a threat unless present in overwhelming numbers: it's too easy for warrior types to parry and cripple the limb.
* If you're adopting published adventures from other game lines, you'll need to throw in a lot of curses, riddles, evil runes, and obstacles. Go crazy with that stuff.

More as I think of it.