I don't "hold" my breath, I just keep attempting to inhale, even when my lungs are full. For some reason, it feels like it's doing more. Something I also do is a quiet pant (like a dog, but so you can't hear it) when my lungs are full, it feels like the smoke is moving around more, and getting more thc to "stick". it all sounds silly but it seems to work better than plain old holding your breath.

My buddy can hold his breath for about a minute and a half tho, it's pretty funny to see him walk around my house and come back a while later to just blow a bunch of smoke out.