Congratulations on trying to become healthier!
Basically, healthy food is food that is in it's original state, not processed, not with lots of other additives. For an example: think cream of mushroom soup. The canned stuff has a few small mushroom pieces, and about a dozen other ingredients and has been cooked and canned and super-heated, and contains unnecessary ingredients. Now compare that to a homemade cream of mushroom soup. It will have mushrooms, sauteed in a little olive oil, and a soup base made of some butter, flour and milk. 4 ingredients. When you know what is in the dish you just made, when you controlled the ingredients, it's better. And when you use good ingredients like real butter, real parmagiano cheese, etc., you can use much less because the quality is far better.
So take a look at your cupboards. Are they filled with packages, boxes, seasoning packets, canned meals? "Just add water!" kind of stuff. Look at your fridge and freezer. Are they filled with frozen convenience foods and bottled sauces?
You don't need to eat plain lettuce. You can make a beautiful salad of fresh baby spinach leaves, orange segments, and some almonds. Substitute different greens, fruits and nuts for a change. Make a simple salad dressing: 1 part extra virgin olive oil, 1 part of either real pomegranate juice, and a little black pepper. You can substitute red wine vinegar for the juice, or try different juices.
The most important thing is: the food should consist of simple ingredients. Cheese should be made from milk, not cellulose and things added to "prevent caking". Salad dressing should be made from oil and juice or vinegars with herbs if you like. Spaghetti sauce should be made from sauteed onions and/or garlic, crushed tomatoes, oregano and basil, not corn syrup and fake things. Just think "simplicity".
A really good salad is: kale (drop it in boiling water for about 3 minutes, rinse it under cold water, chop the leaves but discard the tough stems), blueberries, chopped tomato, edamame beans (soy beans), and some healthy nuts (almonds, cashews). You can add other dark berries and also add pumpkin seeds or sunflower seeds. Drizzle over some pomegranate/oil dressing, and it will be filling and delicious.
Combine chopped turkey with chopped apples and raisins, stir in a little bit of yogurt and spread it on whole grain bread with fiber. If you eat fruit, combine it with some unsalted nuts like almonds and cashews or pistachios.
Take some of your go-to meals and try making them without cans or mixes (except for things like canned tomatoes, or black beans, etc, as long as they are only tomatoes or beans, no sauces or chemicals).
Make a big pan of roasted vegetables: root vegetables are good. Potatoes, sweet potatoes, carrots, parsnips, onions. Cut them all up into similar size chunks and drizzle with a little olive oil. Roast them at 425 degrees until they're browned and tender (toss them around a couple of times to keep the cooking even). Make as many as you can. Then you can puree them, and add in a little pure chicken stock (like Kitchen Basics brand, not a canned broth), and you'll have a really filling soup. You can throw some of the roasted vegetables into scrambled eggs, or put them into a wrap.
Good luck!