To some extent, the exact technique you use is a matter of preference.

There's one useful tip to try though, which was passed on to me some time ago. It is to not follow through too far. So, on a long putt, regardless of the length of your backstroke, only let the club head go max 2 to 3 inches past the ball.

Simply by doing that, you will accelerate through the putt. Give it a try.....