I see a lot of golfers who have decent putting strokes, but are horrible putters because they lack some basic green reading skills.
Like many things in golf, reading greens is extremely difficult to be great at it, but very simple to be decent.
One of the most common mistakes I see people make is not reading the last 4 or 5 feet on putts of 20 feet or more. When the ball gets near the hole it will be losing it’s speed, so that’s where most of the break will take place. So always read what the putt will do at the end.
Always look how much of the hole you can see standing about five or six feet away from it. This will tell you how severe the break will be at the end. The way you do this is to find the lowest part of hole (the lowest part of the green near the hole) and stand in that spot about five or six feet from it. If you can barely see into the hole, the putt won’t break that much when it dies near the hole. If you can almost see the bottom, that putt is going to go sideways and fall of the table when it gets to the hole.
Plumb bobbing is the most over used and and misused green reading tools. There are two reasons why. First, it only works on putts that break only a little. On a 10-15 foot putt that breaks two or three feet or more, if you hit it with speed that dies at the hole, plumb bobbing will only tell you the putt breaks about one foot to 18 inches. Second, if you don’t place the shaft directly in front of the eye you are keeping open, you may read the putt to break the wrong direction. In other words, if you hold the shaft up even an inch or two to the side of your open eye, it can tell you to aim at the right edge of the hole, instead of the left edge.
The important point here is everyone loves to copy what PGA tour players do on TV. How many times do you see a PGA Tour player plumb bob? Almost never. The only time it is used is when players are deciding whether a short putt is to be played just outside the edge, or right on the edge.
To rehash, always find the low spot on your putt whether it is 40 feet or 4 feet. That will help you with both line and speed.