If the engine is out of the vehicle I use a dent puller. Another way is to use a punch, drive the edge of the plug into the block a little bit so the plug turns sideways, put a pair of vice grips on the plug and pull it out. If it is stubborn use the round side of the vice grips like a the end of a claw hammer pulling a nail and kind of roll it out like pulling a nail out of a board.
John