There is no optimal running cadence for everybody, but yours is probably too slow! Most successful distance runners have a cadence of 180-195, with the best runners being at the upper end of that range. The best way to increase your cadence is to use a metronome. Here is a great article by Danny Dreyer of Chi Running explaining how to use one: Running with a Metronome (this will open in a new window). And below is a video explaining how to use the metronome that Chi Running sells (I like these for running - and I get nothing for recommending them). You can also use a FINIS Tempo Trainer, but you have to do some math since that timer allows you set the time between beeps (as opposed to the beeps per minute).

Increasing your cadence typically forces you to land your foot closer to your center of mass, striking with your mid or forefoot, rather than your heel -- under your body rather than out front where it will cause a braking action. It also allows you to take advantage of your muscle elasticity, which is dissipated the longer your foot remains on the ground.