The last 500 ft your attention should shift from inside to predominantly outside the a/c. If glide and attitude look right on pfd then look outside and take a snapshot. Then keep that same picture all the way down until you approach the threshold. You can even put a black dot (whiteboard marker) on the window where your tdz markers are and then just keep that dot on the markers all the way down. At 50 ft start looking further ahead to prepare for the flare. Have a good look when captains fly the approach so you get a better feeling for the picture outside.