After mastering the basic butterfly technique, it is time to put the power into the stroke.
If you use your head in the right way, it will make your butterfly look much smoother and will help you to get your undulation right.
Tuck your chin into your chest when your head is under water, pushing it forward as you pull so that you will be ready to breathe.
Ensure your head goes back into the water before your hands go in again.
This is not easy and will take a lot of practice.
Kicking well will help the undulation as well as pushing you forwards through the water.
Try keeping the legs close but not stuck together.
This will let you turn your feet in slightly and make them more like the tail of a dolphin.
Put your hands in the water with your palms facing outwards so the thumbs go in first, with the elbows slightly bent.
This will improve your arm pull.
Think about the shape of a keyhole - this is the shape you are trying to make with your hands.
Once your hands are in the water, bend your elbows and pull your hands out, then in and then past your hips.
When you lift your arms out of the water, keep them as near to the water as possible. Throw them over the water wide and low.
Breathing time is slim, so breathe out hard just before your mouth comes out of the water.
So, in order:
Pull the arms
Throw your arms over
Breathe every stroke