I seem to have a quandry every time I do a vocal track, especially on a quieter song.  You'll hear just the piano on the intro but when the vocal track comes in you hear a background hiss come in with it.  Very unprofessional and I would like to be able to minimize it if not eliminate it entirely.  Any ideas?
Thanks
 
John B.

Well, on the one hand, there are modern (and fairly expensive) tools like Izotope RX for doing noise reduction that work brilliantly.
 
On the other hand, a bit of manual effort can work wonders. I generally edit vocal tracks to cut out all the space between words. Only keep actual sung words and breaths immediately before words. It can be painstaking precise work, but most audio engineering is.

If you have hiss that's still audible after doing that, you'd be better off solving that at the source. Where is the hiss coming from?

You need to track down the source of the hiss. 
First in the headphones of the audio interface with it disconnected from the computer.