Here's how it's done.
CLOSE GRIP DUMBBELL PRESS PULLOVER - 10 REPS. Hold the dumbbells close together (touching each other) and bring them down to your chest. Press them upwards, and then bring them behind your head for the pullover. Bring the dumbbells down as far as you can, and then pull them back up focusing on contracting your chest muscles during this movement.
DUMBBELL CHEST PRESS - 10 REPS. Just like bench press, except with dumbbells. Use a heavier weight than the first exercise. Since this is a drop-set, be especially careful not to bring the weights down too far -- you shouldn't feel a "stretch" in your chest muscles. Most people should go down to about 90 degrees, but advanced guys who are more flexible
PUSHUPS - 10 REPS. By this time your chest will be BURNT, but stay strong! Do your pushups are normal. Because this is your SECOND drop-set, again make sure your form is on point even when you're really tired.
For a full chest workout, do this 7-8 times. Take 60-90 seconds rest between sets.
And that's it! Maximum "work" and results in your chest and minimum time.