Here are some techniques and perspectives that have helped me:
1) Intermittent fasting. It taught me that I can miss a meal and it is not the end of the world. It taught me what it feels like to have low blood sugar, and what it feels like to be hungry. It taught me how tasty as plate full of mixed greens, a few chicken breasts, and olive oil can taste after a 24 hour fast. If interested, start small and for short periods, and gradually increase.
2) If you have to eat out, or on the run, decide what you are going to eat first, and then go get it. Do not decide at the restaurant/store -- you'll make a bad decision.
3) Eliminate crappy foods from your diet. Start small, practice it, and then add to the list. For example, you could start with catchup. Probably not the worst thing you can eat, but not much nutritional value either. Just learn to say, "Nope, I don't eat catchup anymore." After you get used to that idea, you can expand the list to some really crappy stuff. Sugar, flour, booze, etc. Try to be flexible. Let's say you are stuck in a burger joint. Eat the meat, cheese, and ask for a fried egg on top. Not the best meal, but it beats downing the bun, a plate of fries, and a tub of catchup. Another one I do -- stuck in a pizza place with friends. Eat the cheese, meat and toppings off -- and leave the crust. Not perfect, but it is something (I've given up flour).
4) Find some "go to" foods that are easy, quick, and you like. I always keep these around: eggs, cheese, nuts, hamburger, chicken, cream (I eat a pretty high fat diet), olive oil, mixed greens.