Grounding is definitely important to practice, practice, practice in session. Feet on the floor, walking around, identifying objects in T's office. With all of my clients who dissociate, I have a specific item in the room for them, that they latch on to, to keep them in the room with me. Then we use a lot of descriptors of the items - what do you see, feel, etc.

For clients that are ok with touch, I hold their hand or pat their back. Or I ask for eye contact and that they follow my voice to where I am at.

I've had success with some giving them a crayon and paper to just do something - scribble, doodle, etc, and I talk them through what they are doing on the paper. Sometimes it helps connect them to the present while drawing a picture/feeling from what is causing them to pull away.

I also dissociate in my own therapy sessions with T. I say "I'm shutting down", which for me is the period in which I am beginning to dissociate and am about to throw a wall up between us. My T then clues in to ground me so I don't float away.