I know some exercises for grounding. They help me a lot when I start dissociating. Most of it, for me, involves getting back in touch with my body. One of my favorite little grounding things is Altoids. You know - the really strong candies? I can get one of those, and it gives me a sensation in the here and now that I can concentrate on. Hard to ignore an Altoid...Another is to count blue things. It makes me focus on my surroundings more and gives my brain something constructive to do.
You could also look up "mindfulness". It's the practice of being exactly where you are at every given moment.

My husband describes his alters as...parts of him that he can't be himself. He's working towards integration, where everybody can just be Jon. Right now they're all working together inside and he's in charge and it works really well. Before they would take turns being in charge, and sometimes they fought about it. Usually, when something came up he didn't know how to deal with, someone else would come to the front and handle it. It's gotten better as he's learned how to cope with stress and he's worked through some of his issues. As he learns how to handle daily life, they can all work together and nobody needs to take control anymore.