By increasing the weight you work with, you can
increase the intensity of the exercise and provide more overload to your muscles.
You can add forced reps to
increase the intensity of the exercise, given that you have a good spotter.
To
increase the intensity of this exercise, hold a dumbbell by each side.
Perform 3 sets of 12 reps.. Once your strength improves,
increase the intensity of the exercise by holding a weighted medicine ball between your feet.
You can also hold a weight across your chest to
increase the intensity of this exercise.
Any time you go from standing down to the floor and back up,
you increase the intensity of the exercise and, best of all, this one requires no equipment.
The easiest way to do that is to
increase the intensity of your exercise and cut out unnecessary calories such as junk food and soft drinks.