The No-Weights Workout: Dips
When doing dips, push up with your core and glutes, not just your arms. Lean forward to work more of your chest muscles; lean back to work your triceps.
Make it Hard
With your hands on the backs of two chairs, slowly lower until your chest reaches your hands, then push up. Keep your back straight.
With your hands next to your butt on a bench and your feet out front, lift your body, supporting yourself only with your hands. Lower almost to the bench; push back up.