The easiest way to get back into butterfly shape is with fins, working on streamline kicking and really getting the body motion down. After getting used to the motion, take the fins off and continue to work on the kick. The kick is often an underemphasized part of butterfly swimming, but a strong kick will help you to get your arms over the water. Add in drills such as 3 strokes right arm, 3 strokes left arm, 3 strokes together. A good drill to do is 4 kicks, one pull. As your upper body gets stronger, you can start lessening the number of kicks and eventually work your way to a normal, 2-kick butterfly.