With fruits and vegetables, the fresher the better, so include local, fresh, organic produce as much as possible. Even though I say organic, the organic debate is far from conclusive. Shop as frequently as you can, so that your routine uses supermarket produce as soon after purchase as possible. Keep cooking times down to a minimum. Don't rule out soups and casseroles, but 'balance' with a good dose of rawness - fresh fruit or salads and freshly squeezed juices.
Frozen vegetables can contain more nutrients than some fresh produce, so they're a useful stand-by.
Another simple and, to many, surprising target, is keeping your gut bacteria healthy. Recently it has been suggested that they're also involved in the production of butyrates and other by-products known to reduce the incidence of certain cancers, digestive problems such as ulcerative colitis and heart disease. Antibiotics strip the gut of its good bacteria and so does a generally unhealthy diet. Even so, much scientific and anecdotal evidence leads me to believe it's well worth including probiotic bacteria in your millennium diet. People with irritable bowel syndrome, Crohn's disease or rheumatoid arthritis may react adversely to these bacteria, so check with your doctor before you take the acidophilus pills.