Depends on where I am as well as the type of sushi. In Japan I usually put a tiny drop of soy sauce and have more wasabi, even if wasabi is already in the sushi itself. I never mix the wasabi with the soy sauce.

If there is already a sauce I just use wasabi. Of course pickled ginger is a critical ingredient for all of it.

There are variations. Japan (Tokyo, Osaka, Kyoto) or North are different, The US is very different, Peruvians (Nobu et al) are different again, and Brazilians (inexplicably with cream cheese in sushi ('Hot Filadelfia' anybody) have it different too. Those variations have me not use wasabi at all for some of them, use more soy sauce in some than others (the more vinegary the sushi rice is, the more soy sauce I use).

Thus, I have not fixed habits except: Never mix the soy sauce and wasabi!