When you watch professional golf on television, you'll see players crouch behind their ball on the green, cup their hands over the sides of their face, and read the putt. On the tees, you'll see players holding a club on the line of their shot. In the fairway, you'll see players take practice swings or abbreviated backswings.
They're reminding themselves to focus.
Part of a consistent pre-shot routine is the reminder that you "kick in" to focus. The golfer cupping his hands over the sides of his face is blocking out distractions, focusing on the line of the putt. Lining your shaft up with your target may serve as the reminder visualize the shot. Taking practice swings reminds a player to focus on the sidehill lie she's facing.
Incorporate a "focus key" - something small that serves as your reminder to focus. It may be something small - wiggling your toes in your shoes as you stand behind the ball - or something larger - revising your pre-shot routine to incorporate time for visualization. Just focus.