I was introduced recently to a new drill for helping to improve your catch and hand position in Freestyle. It doesn't really have a name so I'm calling it the "dip and reset" drill. The idea behind this drill is that it works on your hand entry into the water. It helps you maintain a high elbow throughout your entry.
There is a misconception about the proper breathing for Butterfly. Many swimmers tend to come out of the water as much as they can when breathing in fly. This causes their hips to sink in the water meaning they have to expend additional energy to drive their hips back up to the surface. The result is usually a short pause between each stroke. That short pause, even if it's just for a split second, can throw off your entire rhythm.