The key is to pay attention. You find yourself asking "is this ok?" quite a bit until you learn their natural reaction to things. For me, the most important thing is eye contact. I can tell in a heartbeat if my H has disassociated. He literally looks like a completely different person. Pay attention to that. If he "disappears" then talk to him and bring him back. Stop if you need to. Most importantly, have a long and detailed talk about what to do if things get weird BEFORE you do anything new.

Good luck