It's not that important to stand like Jack Nicklaus, but you definitely want to listen to the Golden Bear's advice on how to hold the putter. In his book, "Putting My Way," Nicklaus explains: "To me, the most important consideration in putting is consistent fluidity of stroke, and grip firmness has a major influence on this." Most amateurs grip too tightly, he says. He recommends gripping the putter just firmly enough so that you can control its head path and face alignment, but not so rigidly that it can't swing naturally with its own weight and momentum.
Nicklaus also recommends applying exactly the same grip pressure on every putt, no matter the distance or angle. And he warns you to be careful not to change the pressure during the stroke itself, which will totally mess you up [source: Nicklaus].