K-cup insert removed. Clean with hot water as needed.
On the bottom of the K-cup insert is a tapered needle that punctures the bottom of the K-cup. On the side of it is a small hole. Use a paper clip (or similar) and insert it in there to remove any scale, coffee grounds etc.
Next is to clean the top needle. It is trickier since it is somewhat hard to reach around the sides of the needle. There will be three holes around the needle. Open the Keurig all the way, and again use a paper clip (or similar).