Level 18: The green block clone cannot jump, and the yellow block clone won't stop after you press either the left or right key, but jumps, so make sure the green gets to the exit portal before you get the yellow to the other exit portal, and keeping the clones from falling or touching the spikes would complete the level.
Level 19: You'll need to get your yellow block clone to land on the red block clones and jump off of them to collect the little cyan square without touching the spikes.
Level 22: Move all three clones to the left but don't let the green fall to the lower platform. Then, get your top white clone (but not the bottom clone) to jump out of the pit and onto the platform. Move the green to the left and stack it on the white, and move the stacked clones to the right to get the green to the red exit portal. Finally, get both clones to the exit portal after the clone on the left collects the cyan square without touching the spikes.
Or, scroll down to watch the walkthrough of the puzzle platformer, Jumping Clones, to help you on a level you're stuck on.