Your ball positon should match the low point of your swing, so it changes with each club and depending on whether you want to hit the ball regular or with a special shot like a draw or fade
Breaking putts can only enter the hole in a limited area; by imagining the hole with a piece cut out you can envision the area of entry
On tough shots don't let tension and pressure ruin your frame of mind, create a line of commitment away from the ball where you do your work before you swing