I have a set of moral guidelines for my dwarves.
1. A dwarf shall not use wood unless absolutely necessary. Generally this means wooden beds and burning wood for charcoal if there is no coal or lignite. There is no use of wood as decoration, ever. The only exception for this is a possessed strange mood, as the dwarf has no control over what he's using and we blame the evil spirit. Secretive moods, etc, that use wood are immediatly locked in a room/workshop and allowed to starve.
2. Dwarven needs come before all other races. We'll trade fairly with our dwarven brethren, and even with humans and elves... but if the humans or elves (or goblins) have something we need, and we cannot give fair value, we take it without hesitating. Often we will give fair compensation next trade season for these actions.
3. Dwarves shall not pass up an opportunity to kill an agressor. If you're a lone farmer planting some plump helmets in the middle of the night (god that sounds bad if taken out of context) and you come upon a kobald, YOU WILL RUN HIM DOWN by Armok and BITE HIM TO DEATH if need be. All but heroic (see below) dwarves are activated into the military upon the onset of any agression. Bad thoughts from this are mitigated by our legendary dining hall which is, by the way, decorated with bones of kobalds and goblins.
4. Armok requires blood. Once a season, a living humanoid must be sacrificed to Armok. If no non-dwarven entity is available to be sacrificed, a dwarf must take his place. Dwarves are chosen for this based on their need for the honor it brings. A legendary miner needs no more honor, but an undistinguished peasant needs a noble death. If a dwarf is sacrificed, his family is forever honored and need not work for an entire generation. (Wives/kids will have no jobs enabled except healthcare and burial duty, and will not be activated when a siege is incoming.
5. Unusable items are not recycled, they are sacrificed to Armok. Every settlement will have a pit of lava (or water if no lava is available) into which all narrow/tall/unusable items are thrown after being looted from the dead. Incidentally this is where the unbutcherable bodies of enemies are thrown as well. If we find a dwarf has claimed an unusable item, to the pits he goes along with his beloved goblin socks. If a Dwarf opens an exotic clothing store, he is put to death with his entire family.
Other than these guidelines, I handle things as I see fit for a map. Sometimes I build elaborate mechanisms for flooding the entryway with magma or water, sometimes I use traps and crossbows, sometimes I just have hordes of wrestlers or swordsdwarves.