Adequate diet and plenty of calories if you're breastfeeding, adequate rest (which may mean lots of naps and less housework), getting out into the sunshine and getting some exercise along with the fresh air, having social support/companionship in due measure, getting others to hold the baby while you accomplish self-care and a little downtime (like for a nice bath and such)--and finding people to talk to if you start to feel signs of ppd coming on.
Exhaustion, undernourishment and isolation seem to be very much at the root of ppd for so many women. So do all you can of the simple ordinary things to keep yourself contented and steady....and get some help in simple ordinary ways, too.
Not sure where, but there is a whole forum here on MDC on PPD--take a look, there's lots of advice there (I'm being lazy--I've gone there a time or 2 but not recently, can't direct you exactly without looking it up).