You consistently pull or push putts because your eyes are either too far inside the ball at address (causing a push) or too far outside the ball (causing a pull).
Position a ball in the little hole in the middle of an old music CD, shiny side up.Address the ball as if you were going to putt it and check where your eyes reflect on the CD. If your eyes are inside the ball, bend slightly forward from your hips until they move over the middle of the CD. If your eyes are outside the ball, bend slightly back from your hips. Eyes over the ball gives you the best view of the line and stops pull and push strokes in their tracks.