In this paper, a methodology for designing efficient energy scavengers is proposed. The scavenger consists of a cantilever beam on which piezoelectric films and a mass are mounted. The mass at the tip of the beam is known as the proof mass and the device is called either an energy scavenger or a beam-mass system. The proof mass is a permanent magnet, where in its vicinity attracting permanent magnets are placed. When a scavenger is mounted on a vibration source, the cantilever beam would vibrate. Due to the vibration of the beam, the piezoelectric films generate electric charge. The generated charge is proportional to the amplitude of vibration of the tip of the beam. It is shown that when the magnets have appropriate strengths and are placed appropriately, the vibration of the tip of the beam can be amplified, thereby the scavenger efficiency is increased. Examples are given throughout the paper.