A lot of people have heard of and use an intermediate spot for alignment.. An intermediate spot is best when only 3" to 4" inches in front of the ball. Generally the width of your putter head. I teach my students to add an intermediate spot behind the ball approximately the same distance. This will improve your alignment. The rear spot justifies the ball position and intermediate spot in relationship to the target. In other words, you now have 3 spot holders to align to the target. If any of the spots are out of alignment you will easily see it regardless of which one it is.
The greatest affect on where the ball rolls after impact is the putter face angle at impact. It has an 83% affect of where the ball rolls while path direction has only 17% affect. If your putter face is square to the target 4" inches or 10CM before the ball and 4" inches or 10CM after the ball, the ball will have an 83% chance of rolling directly at the target. That is the secondary purpose of the 2 intermediate spots. The putter face should be square as it crosses over the first intermediate spot and maintain that square face until the putter face crosses over the second intermediate spot.
Initially practice this from 3', 6' then 9' until you have completed the success wheel of confidence. The more success you achieve from practicing the two intermediate spots, the more confidence you will have on the course when using it. Success breeds confidence, the more confidence you have the more success you will have.