It's fairly straight-forward. Just come up with a weakness or limitation to the superpower of the person above you to make it functionally useless or at least less-than-desirable, then come up with your own superpower.
For example:
Guy1 wrote...
The power of immortality...
Guy2 wrote...
...without eternal youth.
The power of flight...
Guy3 wrote...
...but only to a maximum elevation of 2 inches from any solid surface.
...
You get the idea.
For my power, I want the power of mental telepathy (reading minds, sending thoughts/messages to others, etc.)