Correct level of input to a cubase plugin

I have a doubt for days,
What is the correct level of input to a cubase plugin to work correctly. I have not found the answer in the manuals.
For example: I want to use the cubase compressor and I would like to know the optimal input level for this.
Thank you.

Loud enough that you can get the comp working enough without running out of threshold and quiet enough that you are not clipping the input.

Ok. Thanks for the reply. If the input signal is less than 0db there are no problems.