Is there a rule of thumb with setting levels?

[nvisibl]

forinstance in my own setup I have a bunch of hardware going through a motu i/o 24 with everything sequenced in cubase. so i can set levels at several different points.. i.e. on the hardware units, the motu, or in cubase or wherever else thereafter.

I can sometimes get myself in a guddle say for example like where i've maxed the levels on the motu but some of my hardware volumes are only half way up or just a general mish mash here there and everywhere.

so how is this played, is there a general rule of thumb involved?