I'm conflicted how to use PB at the start, I really don't feel running into combat and using it immediately is the best way to go. I generally do something like (on my phone so abbreviating):

Dk
Twin
Sp

Dk
Twin
<ir>
Sp

<pb>
Sp
<BfB>
Sp
Sp
Twin
Demolish (as pb ends)
Fracture

Touch of death

Then normal rotation of dk twin sp bs twin sp. I always pair demolish and fracture when they need done and redo touch of death when needed. As well as using steel peak and howling fists on cooldown.

I use ID rotation if the mob has < 18 seconds to live which is just dk/bs, twin, id, id, id, sp.