There is technique involved. Start working on a kipping motion, then work on chest to bar pull ups, then dips. Now put them together. The hardest part is the quick motion transition from pull up to dip. You have to put your chest over the bar as quick as possible to change your center of mass while switching your arm position to a dip. You doing these on a bar rather than rings? Try to find a low bar and start the motion by jumping into it rather than from a hang. They are a great power and cardio workout.