When taping and finishing drywall, people seem to struggle most with inside corners. The temptation is to try to work on both sides of a corner at once. If you do that, while you are working one side, the edge of the taping knife or the wet drywall compound (mud) that can build up on its edge will mess up the mud on the other side. It can lead to an even bigger mess at the point where the wall meets the ceiling and three corners come together. There is a trick to it, but before tackling the corners, tape the flats. Then bed the tape in all three corners (two ceiling and one wall), finish-coat one side of each, let dry, and finish-coat the other sides. You can generally do half of a corner one day, and the other half the next. In humid conditions, it can take longer for the mud to dry. The drying time can be problematic on small jobs that you could otherwise finish in a day. To speed things up, use setting compound instead of regular drywall mud from a bucket.