For years now scientists and doctors have been looking into the effects of calcium on the female body, particularly with regard to menstrual cycles and menopause. Enough calcium in your diet can really help with the cramping, bloating (or water retention) and general malaise that often comes with PMS. It is important, however, that you find a balance. Too much calcium in your system can cause problems too, as I understand it.
Another big factor, according to my ob-gyn, is sodium level. If you've ever read Cosmo or any other women's magazine, you've probably seen cramp remedies that include lowering your sodium intake at least a few days before your PMS typically begins. It makes sense--keeping your body hydrated relieves cramping; sodium works against that hydration. So... lay off the extra salty snacks at least 3 days in advance.
Magnesium plays a role in cramping as well. It facilitates nerve and muscle activity by smoothing and relaxing blood flow. Other suggestions include lying on your back with your legs elevated and knees supported, stretching or yoga exercises, breathing techniques (or any other stress-reducing activity) and--my personal favorite—venting my frustration in new and imaginative ways. :P
Seriously, though, the best way to address PMS problems is by preventing them. Thinking wisely about your diet can save you (and your loved ones) many aches and pains later on.
Information verified with http://www.pcrm.org/research/menstrual.html