Like said, PRACTICE PRACTICE PRACTICE....
I CC everyday at about 4O'clock, and have become pretty efficient at one handed draw. Wearing an under shirt or tank, with a regular shirt over that. Two handed draw is much easier, clearing the garment with weak hand, while acquiring grip/gun with dominant hand. Makes for clearing and not catching on the clothing easier. But like said, you may not always be able or want to draw gun in that fashion. Being able to clear clothing and draw with one hand, for me, is much simpler, less obvious, and can be just as quick. But practicing helps. My biggest problem with one handed draw from CCW with IWB, is catching the shirt or under shirt between your hand and the grip. But again, thru practice I have become pretty good at clearing the shirt, or if/when it gets caught during practice, learning to keep drawing thru and releasing the garment.
Hope it helps, and again, PRACTICE PRACTICE PRACTICE