Once you have located the dripping and placed buckets and towels under it to prevent any further damage, the first step is to contain the leak. As water comes into the house it will pool under the ceiling until it can find a way down through a seam in the drywall or register. If the outlet is not big enough it will eventually find another, damaging a different part of your house. To keep this from occurring, poke or cut a hole where the dripping is and allow the water to flow into the bucket you already have set up. This may sound counterproductive, but it will actually keep the leak contained where you can catch it, rather than spreading.
