Your putter is designed to get the ball rolling smoothly. You diminish its ability to do so if you play the ball back in your stance. To roll with topspin, putts should be struck – like your driver – with a slightly ascending trajectory. Put the ball just forward of center in your stance to ensure that this is happening.
There are times to play the ball back, too: when your ball is against the fringe or a cut of rough, for example. Hitting down on the ball introduces backspin, which causes putts to skid and slide offline and with less control.