Judging the slope of the greens is also aided by using proprioceptive information from your feet. If you stand with your feet pointing uphill, the further back towards your heels that you can feel the weight, the steeper the putt. If you are standing upright and you feel the weight on your heels, that means a slope of about 4%; if the weight is on your toes, it’s about a 1% slope.
To get the aiming point, I like the method shown here: http://puttingzone.com/MyTips/spider.html
For the strength of the putt, you should aim for a point about 9 inches behind the hole on the path you’ve decided.
Some people use visualisation to judge the line of the putt. One technique is to imagine that the hole of full of water which starts to overflow. You just have to note the path of the water, and this will be the path for your ball in reverse.
When Tiger Woods was a toddler, his father Earl had him put a ball in his right hand and roll it to a hole. Then he had Tiger close his eyes and roll it into the hole again. He asked Tiger what he had “seen” after he had closed his eyes. Tiger replied that he had seen a “picture” of the hole. Earl told him to always “putt to that picture” before he struck the ball, creating a picture in his head of where he wanted the ball to go. So Tiger’s focus wouldn’t be on the mechanics of the shot, but simply what needed to be done to the best he can visualise. Once he was comfortable with the instant pre-play in his mind’s eye, he’d play the shot.
Jack Nicklaus cited visualisation as the number one secret to his success, and even visualised every shot during practice: “First, I see the ball where I want it to finish, nice and white and sitting up high on the bright green grass. Then the scene quickly changes, and I see the ball going there: its path, trajectory and shape, even its behaviour on landing. Then there is a sort of fade-out, and the next scene shows me making the kind of swing that will turn the previous images into reality”.
Everyone will have their own type of imagery that works best for them, but it all comes down to creating some kind of pathway in your head, and then you just have to try and get the ball to follow that pathway.
Talking to the two pro golfers that I’ve seen recently, I got the impression that visualisation was an area they could improve. With practice, it’s possible to make it almost as realistic as the physical act of putting itself.