The young Tiger was an aggressive putter who often faced comebackers from tricky distances. Today he's much more of a "die" putter, and the ball tumbles into the hole with its last gasp. This slower speed means he has fewer long comeback putts if he misses, and ups the chances that he'll lip instead of lip out.
Good die putters like Tiger hit their putts with minimum pace necessary to get the ball to the hole, so it's slowing down as it reaches the cup. Only by hitting the sweetspot consistently can you program how much speed and velocity you need to make the ball go the correct distance--ideally, 17 inches past the cup should the ball miss the hole.
Don't peekDuring the stroke, nothing moves from the neck up or the belt line down. Tiger's head doesn't budge until the ball is gone. There is no unnecessary body movement that might cause him to miss the sweetspot. The face stays square to the arc longer, promoting solid contact.
Heads or tails?
When you putt, pretend there's a coin underneath your ball. After you've stroked the putt don't look up until you've determined whether the face of the coin is heads or tails. Then swivel your head and look. By focusing on the coin, you're sure to keep your head still.
Find the sweetspot
Practice putting with two Band-Aids stuck on your putterface as shown, leaving the sweetspot uncovered. This will give you instant feedback on whether you're hitting the sweetspot or not. If you hit either Band-Aid the ball will travel only half the distance you expect it to. The more consistently you're able to hit the sweetspot, the better pace and distance control you will have.