i like to go in a zone say anywhere from 5/8 (a little more than half) to around 3/4 up the digital meter, this way, i give myself some room so i dont clip, but its not recording a block of ice.
listen for it, you can hear if you are too hot/not hot enough.. you think you won't know right? give it a shot, close your eyes and play with the gain knob, i bet you will come close!