keep it out the red, leave as much headroom as you can. Trouble is, when producing at home, its great fun sometimes to run everything a little bit hot as it were and have it all pumping, but its not so great when you get masters back asking you to redo them because everythings been maximised and the engineer cant do anything with your blocks of audio. It's something that is learnt over time i think, well without being too obvious, and something that common sense plays a big part in.