Zinc is a good supplement to take, as it is thought to benefit the prostate gland generally. You should also increase your intake of Essential Fatty Acids (EFAs), which reduce inflammation in the prostate. These are available as fish oils or flaxseed oil.
Pumpkin seeds contain both zinc and EFAs and are therefore a good snack food to munch on. Reduce alcohol consumption to reduce inflammatory processes in the body.
Lose any excess weight, as being overweight is associated with worse symptoms of enlarged prostate. Sexual abstinence and withdrawing without orgasm can apparently contribute to enlarged prostate and should be avoided.