Difficulty - Easy
Muscle Groups Addressed - Upper Pectorals, Shoulders, Triceps
Let's start with something relatively simple. The decline pushup is a great, effective exercise that can be performed virtually anywhere.
All you need is an elevated surface. In this case, I simulated the incline with a staircase at work.
The standard decline pushup should have palms flat on the floor, shoulder width apart, and feet resting on a 1'-2' tall elevated surface, so that the body forms a rectangle with the floor. Keep your core tight, head down and slowly lower the body to the ground. Come down to a few inches above the ground, hold for a second, then drive the body back up to the starting position without locking your elbows.
The exercise can be adjusted in multiple ways to work different muscle groups. You can engage the triceps more by bringing the hands closer together, or the outer pectorals by spreading the hands farther apart. Based on the height of the incline, you can work higher on the pecs (high incline) or lower on the pecs (low incline). For the more advanced move and to really work the core, try lifting one leg in the air.