Learn to pull with your left or push with your right hand. Pulling means back of the left hand at the hole, pushing I mean palm of the right hand at the hole.
Determine which hand is your dominant hand by hitting putts one handed. If you can control the face better with the right hand use a slightly firmer grip with the right hand and looser grip pressure with the left hand. If your left hand is dominate use a firmer grip with your left hand and looser grip with the right hand.