-Slowly make a circle around him then fire when he goes to spit out fire. If he spits fire, just wait and when he is done try again until you catch him.
-Don't try to capture it at the beginning but wait until he spits fire up. Wait until the fire goes onto the floor, then choose a spot where Charizard is going and use your capture device to take damage on those fires. Repeat at least two to four times, then circle as fast as you can to capture Charizard.