Step #1 - Eat Healthy
Yogurt is a fantastic option, but be wary of sweetened yogurt. Like I said, sugar damages your immune system, so it isn't really helping anything. You can buy plain yogurt and sweeten it yourself with some fruit or fruit juice. My kids like apple sauce mixed into theirs. Real the labels, however. Some of the cheaper brands will only contain one strain of bacteria, while others will have as many as five. Go for the higher number.
Bone broths are made from cooking bones in water for several hours, allowing the vitamins and nutrients to be released into the water. Chicken stock, beef stock, and fish stock are all bone broths. These real stocks cannot be purchased from the store. The store bought stuff is not real and usually contains MSG. They aren't hard to make though and are certainly worth the nutritional benefit, which includes calcium, phosphorus, magnesium, potassium, sulfate, fluoride, collagen, and more! (In fact, ladies, there's even been research that the collagen in bone broths will reduce and remove cellulite! I'm serious! I've read about several people who have tried it successfully.) Google "bone broth" and you'll be able to find countless recipes. Use it as stock in soup recipes. Chicken stock is called "Jewish Penicillin", because of its miraculous effects on fighting off colds and influenza.