Advanced front crawl is for those who can swim quite a few lengths without having to stop for a rest.
The aim is to make each stroke longer and more powerful.
Increasing the power from your legs is like changing up a gear in a car, but the approach you should take depends on whether you are swimming for shorter or longer distances.
Fast legs are for short distances and a slower kick for longer distances.
Count how many leg kicks you do for a length of the pool. Then try changing the speed and count again.
You should be able to turn your head smoothly and regularly.
Practise breathing in different ways.
If you are used to breathing every two strokes on your right hand side, try doing this to your left.
Better still, practise breathing every three strokes. This will help you to swim a better and faster stroke.