For me, deep breathing helps a lot - focusing on the breath going in and out, the feeling of my body, the way my ribs move, etc. It takes me out of my head and really helps me get past it. Also, I find myself more likely to cry spontaneously the longer I've held it in. When that pressure builds up and I get a chance to let go in private, I try not to control myself, instead I feed in all those emotions and let the tears roll. Eventually I just run out of cry. A couple times letting the pressure out like that and the feeling of crying over anything seems to let up.