Try to get to a stage where you don't have to refer back to your paper. Do this by thinking of your chords as patterns or shapes. E.g. The D Major chord looks like a triangle or arrow pointing up the neck of the guitar.

Mostly memorizing chords will be done through playing songs, but you can start off by using little tricks. I'm sure most people at some stage in their childhood played join the dots. Use the same sort of idea when memorizing these chords. By joining the dots, you'll make certain shapes, those shapes will remind you of certain things. Probably the easiest to remember would be "D Major", D Major makes a simple triangle shape when you join the dots.

Place your mouse over any of the boxes on this page, then you will see a graphic animation on how to remember these chord shapes.