pawns are good cannon fodder, when properly deployed, as an opponent might not like to take a pwn with a piece if he/she thinks that pwn is protected by another pwn.
KNs are excellent for 'unseen' sorties, have won (and lost) a few Qs because the Kn wasn't spotted.
Rs belong to open lines just as in normal Ch. but I would call an open line any line where yr own pwns have been exchanged, even if an opposing pwn is still on that line.
Bishs should be in the open or just 1 move away from that, ie=behind a pwn yr about to push on.
Qs like to be in the open too, but beware of squares where a Kn might lurk unseen.
I find bluffing can be quite helpful, I remember a game where I challenged the K with an unprotected R, knowing my opponent was worried my Q was behind it. He didn't take and moved the K in the open just like I hoped, 2 moves later my Q took it as he moved where he thought my Q could not get to. But my Q wasn't where I made him think it was.