How do I center clay?

I'm in a ceramics class. We've learned how to throw clay but I still cannot seem to get mine perfectly centered no matter how hard i try. I use the technique of putting one hand on top and the other on the side, as it is tucked into your thigh. I use clay thats been pugged to make sure there is no air, i throw it down and try to get it into a little dome, then i wet the clay and start the wheel. After a while I seem to get it somewhat centered, though I can tell its off. If I continue to try to center it it just seems to fight me and become more off centered when I started. Help