Use smaller bowls. Invite yourself to have as many seconds as you want, but don't pile an unknown amount of food on your plate and then feel like you have to eat it all.
For me, cutting out meat worked. I'm not hardcore vegetarian, but it really cut down saturated fats and made me include more veggies. Cutting out bread-type carbs really works, too. Soups have always helped me feel like I'm eating a meal that makes me full because it's hot and fills my stomach with more water-based volume.
Instead of packing a sandwich for lunch, I pack a bunch fruits you can hold in your hand and don't need tupperware -- oranges, apples, bananas. Squares of dark chocolate, hot tea or chewing gum for snacks during the day is my best trick.
It really depends on what works for you. I believe in you! Feel free to experiment, and don't ever feel like you failed. It's because that method wasn't working for you, not the other way around.