HIIT - High Intensity Interval Training
Go inside any big fitness center in America and you will see a large majority of people walking around aimlessly, and the rest are spending all of their time on treadmills, elliptical machines, stationary bikes and exercising with free weights with no real understanding of what to do. These types of exercise are fine as long as you follow a routine that progressively pushes you harder each week instead of doing the same thing everytime. Having a personal trainer will not only help you create a personalized workout routine but would help you to push yourself further than you would be able to on your own.
The best form of exercise I have found is called high intensity interval training (HIIT). It involves repeated bouts of high intensity effort alternating with recovery period.
Do all three exercises with out resting, and then repeat it three times.
This is a starting point. As you progress, we will go way beyond this.
Squat to Overhead Press
Medicine Ball Side throws
Pushup Mountain Climber