Two forces are applied to a ball as it rolls across the green, they are gravity and friction. When reading a putt you first should look at the green complex and surrounding areas as you approach the green. You are looking for the overall slope of the green, back to front, left to right etc. This helps you understand how gravity will effect the ball. Once you understand the green complex you can start looking at the green between the ball and the hole.
Because downhill looks will always read less break than there truly is, we always want to read it from the low sides. If it is an uphill putt, don’t waste your time behind the hole, read it from behind the ball for the break. Then move to the middle of the line on the low side, standing far enough back to see the ball and hole. This is where you get the feel and judge your distance control. If you have a down hill putt, read it from behind the hole looking up towards the ball. It’s like reading a book, when you get tired and the book starts laying down in your hands you can’t read the words as well as when it’s held up. Find your line from behind the hole, move to the side again for distance control, then set up and trust your line from your read.
Finally when reading the putt, pay attention to the grain. Grain creates friction, if it is down grain, there will be no friction, into the grain or side grain will apply friction, a slowing force to the ball. Grain is the direction the grass is laying and can be seen as shiny or “down grain” and dark “into the grain”. The ball will be effected by it and the ball will move the direction the grain is going when it is moving slowly. The ball moves its slowest at the beginning and the end of the roll, and grain that is into, or laying at you. can cause the ball to hop at the beginning of the putt and during the roll slowing it drastically. But remember top dressed greens or greens at 12+ on stimpmeter will not have a lot of the plants leaves touching the ball, so grain will be minimal.
So remember, you’re looking for gravity, grain, reading it from the low side and getting the speed from the side. Putt all those observations together, commit to your line, good stroke and roll them in!