Items on dwarves catch fire
Just like how DF was before 0.31, clothing and carried items on dwarves should catch fire upon contact with other burning items or magma. As before, dwarves with flaming clothing will run about flashing red and trailing smoke. For some reason, this was removed in the updates, but should be relatively easy to implement.
Furniture and buildings catch fire
Furniture, floors and walls made of wood or other flammable materials will catch fire when adjacent to other flaming furniture/walls/floors, flaming items and magma. Wooden workshops will burn down, and wooden constructions will be rapidly consumed by a spreading inferno.
Burns
Currently, the only way a dwarf is damaged by heat is when his flesh starts melting. Instead, wounds should also be caused by direct contact with sufficiently hot items and liquids (i.e. magma). Upon contact, burn wounds are immediately dealt to the affected body part, varying in severity depending on the temperature. Due to the cauterizing effects of burning, burns will bleed little, and death by bloodloss will be uncommon except after a prolonged time without treatment. With a severe enough burn wound, the body part can completely burnt off.
Automatic dowsing of fires
To prevent all fortresses from collapsing completely in blazing infernos, the dwarves will be slightly more sensible in their actions regarding fire. Burning areas and tiles with flaming items on them will have an increased traffic cost, or be completely unpathable just like magma-containing tiles. When a dwarf catches fire, he will immediately attempt to take a bath, hence quenching the flames. With the right labor enabled, dwarves may also attempt to put out flaming tiles and dwarves with buckets of water.