The number of push-ups a person does at night depends on her fitness goals and experience level. A beginner should start with two to three sets of 10 repetitions each for a total of 20 to 30 push-ups depending on her current fitness level.
Men's Health suggests that anyone who has trouble completing 10 repetitions should take the number of push-ups she can perform and divide that by half. Next, perform five sets of that number of push-ups, resting 60 seconds between each set. For example, anyone who can only do eight push-ups should do five sets of four push-ups, then rest for a couple of days before repeating the exercise. Building on this foundation allows the person to increase her push-up repetitions as she gains strength.