Right before I start the putter back, I think about making solid contact. This brings your attention to the back of the ball and helps keep your head still at impact, which is a must. Many amateurs take a peek down the line too soon, and that can cause all sorts of mis-hits.
You should never get set over the ball and then aim your putter face. If you do it in that order, you can easily lose sight of your intended line. Instead, aim the face down your line first, then settle your body into position.