Select a weight that will allow you to complete 10 to 12 reps of the Pullover in
good form with the last rep being the last one you can possibly complete without help. In other words, go to failure. Immediately reduce the weight approx. 30% and do another set without resting. Take that set to failure for however many reps you can complete. Again immediately reduce the weight approx. 30% and do a third set without resting. Take this third set to failure for however many reps you can complete.
Now rest about a minute and do a compound exercise for your lats. Let's use the Reverse Grip Pulldown for this example.
Your lats should be fairly fatigued if you performed the Pullovers as intensely as I described. Select a weight that allows you to complete 10 to 12 reps to failure. The weight you'll use will probably be significantly less than you normally use because of the pre-exhaust we did on the Pullover. Now just like on the Pullover, complete your first set to failure then immediately reduce the weight approx. 30% and do a second set without resting. Again immediately reduce the weight approx. 30% and do a third set to failure without resting.
This is a pretty intense technique and should probably only be utilized very sporadically. In fact, I would recommend waiting at least 7 days before you train lats again after a session of "Triple Drop Pre-Exhaust".