Replace your "bad foods" with healthy alternatives that look (nearly) the same. I haven't had a milkshake in months since replacing them with delicious green/almond smoothies (which incidentally is the only way I will put kale in my body). Another favorite is veggie chips to replace potato chips.
Carry a water bottle with you everywhere. When you have water near you, you'll start drinking it even if you don't think you're thirsty. I started doing this in college, and my water consumption went through the roof. It also helped me develop a stronger sense of my hydration levels.
Wear workout clothes. It makes the decision to go to the gym that much easier.