How do you recover a dying peace lily?

It depends on why it's dying. Is it too wet or too dry? Too much sun or not enough light? The soil should be allowed to dry between watering. Avoid direct sun, it's a lower-light plant. Water and light are the most important factors with any plant. Concentrate on getting them right.

The best conditions I've found for mine personally are a few feet away from a south-facing window in the north-east part of the US, with white curtains that let light through. Allow the leaves to droop slightly between watering, but too much drooping and you'd better water more heavily once to bring it back.

And to quickly bring it back to life, put it outside for the summer on the north side of your house (in the northern hemisphere) and water once a day, fertilize once a month with a general fertilizer like miracle grow.