Getting good at lag putting is all about practice and all about feel.
There’s no quick way of getting good at it. You just need to put in the time on the putting green.
The key thing when it comes to technique is to keep the triangular shape between your hands and shoulders and get that pendulum swing going.
You really don’t want to become ‘handsy’ with it because that’s when you start struggling with distance control and you’ll either hit it too hard or not hard enough.
The key really is to get all your big muscles in the right place and keep the triangle as your swing the putter back and through.
My best advice would be to practice a lot of lag putting on the green whenever you get the chance. Drop down balls at various distances and really get a feel for the speed of the greens. It does take a lot of practice.
There’s not really one specific drill you can do. I’m not really a big drill guy anyway. The key is getting the feel for the pace of the greens ahead of your round.