The first part of the process that I do is I stand behind the hole to firstly decipher where the ball is going to go. I'm trying to see which side of the hole is higher. Whichever side is higher is where I would aim the ball. Sometimes it's not easy to see which side of the hole is higher and that's where I would look at the shape of the green and see where the green is going uphill and downhill.
I would also look at the fringe to give me clues as well to see how the green is shaped. Once I've worked out which side of the hole is higher, I will then go back behind the ball and check also the shape of the green. Sometimes it can be obvious and you don't need to check both angles but other times there could be more than three breaks in one putt.
Between the ball and the hole, I'm looking for indicators of slopes and mounds that will affect the putt. Once I've worked out any additional breaks, I will then calculate this to my final conclusion. I will also step out the putt and feel the breaks with my feet. This is actually the best way to get a real feel of what the putt is doing. I will also step on either side of the hole and test with my feet if I'm unsure of which side of the hole is higher.
When assessing my final conclusion and I realise that the right side of the hole is higher but the first of my putt there's a slope that will make the ball go right, I may have to just hit a straight putt. However if I notice that the first part of the putt has a more severe slope to the right than near the hole, I will in fact aim more left to counteract.
In conclusion you will get better at reading the green through experience such as ensuring you step out the putt to feel the break as well paying close attention to the shape of the green.
If you'd like any help in reading greens, book in for lesson and I'll walk you through step by step.