Note: If you don't have powerlifting boards, just use anything that approximates the height.
Week One: 4 second drop to a 5-board
Week Two: 5 second drop to a 4-board
Week Three: 6 second drop to a 3-board
The Assistance Phase
Week Four: Band across the hip for assistance on the way up.
The Limited ROM Phase
Week Five: Push-ups to a 5-board
Week Six: Push-ups to a 4-board
Week Seven: Test your push-up max!
Each variation can be done for 4 to 5 sets of max reps (until failure). For the best results, perform each variation up to 3 times a week, each time trying to hit a new rep max.