It's easier to ruin an otherwise healthy diet with unhealthy snacks, because unfortunately most snacks fall into this category. But there are some good snacks foods out there as well.
Fruits and mixed nuts are very healthy and good for your digestive system. You can have a small snack in between meals and still be able to eat your dinner with the family, providing you don't overdo it. Choose snacks that are less filling but still nutritious.
Say you're on the go and don't have time for lunch. Yogurt, bananas, graham crackers, and granola bars will help curb those hunger cravings better than a hot dog or bag of chips will, and they'll give you energy. Sitting at home watching TV and wanting something to eat? Try carrots and dip, pretzels, or some dried fruit. Even canned fruit with low sugar is a good choice.
When you go to the grocery store, be sure you've eaten first. If you go on an empty stomach, it's more likely that you'll be tempted to buy unhealthy snacks. Shop for things like fresh vegetables and lean sandwich meats. Popcorn can also be a healthy snack as long as you don't add too much butter and salt to it.
Healthy snacks are great, but you still need to make sure you eat healthy full meals as well. Snacks alone won't provide you enough nutrition, and you could fall back into some bad habits. So snack healthy, but don't depend on them.