My mate told me a great way, its like saying the words of command and carrying out the action (2-3 is just counting the time, for anyone who has not done drill before

)....
Hang on the bar, "DOWN, 2-3, QUATER (up), 2-3, HALF, 2-3, QUATER (up again), 2-3, UP, 2-3, QUATER (down), 2-3, HALF, 2-3, QUATER 2-3, DOWN, 2-3, QUATER (up) etc..."
Hope everyone understands!
It is excellent for Royal Marine POC, as the pullups/situps/pushups are all done on a bleep, so this method is really slow, so when you come to doing them on the faster bleep, they are easy peasy. And if you do them in your own time (i.e. as fast as possible) then it is even easier.
Could try this method with pushups and situps aswell, if you want.
Good luck
James