This tip comes from Masters champ Jackie Burke, widely regarded as one of the best putters of his day and, perhaps, ever.
The tip is relatively simple: practice two-footers with your left hand only. Start with two-footers, and bang several dozen of them in. It may be difficult at first, but your stroke will become smoother as you continue. You'll strike your putts more solidly. This helps to eliminate the dreaded breakdown of the left wrist.
When you're confident in your ability to make the two-footers, move back to 10 feet. When you're comfortable with that, put your right hand back on the putter. You'll be surprised at the difference.
This drill works for cross-handed putters, "claw grip" putters, and more. According to Burke, it may be the quickest way to turn you into a good if not great putter nearly instantly.