There's one big piston that goes up to the boss which you can get onto by climbing up the other pistons. There's a piston near the one you use to get to the boss that goes up just as high, and you need to use another piston next to it in order to get on.
Basically, use the pistons and try to time your jumps so that you're jumping from the piston's tallest point while the one you're aiming for is moving down. Hope this helps.