I use Lithium grease on the bolt rails. Mind you it's not the spray stuff. I just apply it lightly with a Q-tip.
As for the other moving parts
Leave your Gas piston dry as oil will just attract more carbon build up
I wouldn't recommend lithium grease on your firing pin as it might attract debris and cause a slam fire. Keep your firing pin clean and maybe a little light oil.
Lightly oil your bolt/carrier but lithium grease is probably not the stuff to use, I use synthetic 5w30 oil.