I'm a big believer that simply by changing your habits, one small habit at a time, you can change your life. Whether that be to lose weight, to start a business, to run a marathon... It can all be broken down to focusing on those seemingly little things you do on a daily basis. Work on a habit for a few weeks and it will turn into a subconscious act - you will naturally do it without thinking.
Mornings habits are the easiest habits to form because we generally follow the same routine every morning. So I'd say, start with your morning. But take a step back and look at your day, you'll notice you have routines during other parts of the day as well. Like the evening, which is where most of us get de-railed with healthy eating. When you are used to something at a certain time, you crave it, or if you don't crave it, its a habit so its what you reach for. I used to always have a bowl of cereal in the evening. That is another habit I switched up. I can't do the "no food past 7pm thing". It doesn't work for my body. I go to bed hungry, then I can't sleep, then finally at midnight I go get something to eat. So I have stopped trying to do that. I also can't just have fruit, it needs to be more substantial or more "carby". I will have a nut and seed bar (I just have to watch I don't eat too many of those) with a glass of almond milk or cheesy kale chips or roasted chick peas. I've dropped my craving for cereal and find it easy to go to healthier options.
Think about the difference just a couple simple changes can make over a year (in this case breakfast and evening snack). Once these habits are second nature, you can start looking at changing other habits, another example being lunch and always having the base of it be a large salad. Just switch it up often (different proteins, greens, fats) but always have it being a big salad (or homemade soup/stew in the winter).
Habits I am working on now:
homemade protein bar for breakfast
go for a walk/jog every day
rowing machine for a min of 10 minutes every day
evening snack - alternate between a few healthy go-to snack options for the evening
Tips for Success
Start with small changes. While working on my rowing habit, I started with 5 minutes each day. Before the habit is actually formed, it is easy to not do it. So by making it 5 minutes rather than 10, I was more likely to just do it. I then gradually increased by one minute at a time. For my evening habit, I chose things I still enjoyed and would satiate me. I needed "carby" things so eating veggies at night would not have worked. I simply found healthier versions of the types of things I liked.
Commit to doing that habit for at least 21 days. It will be harder to do everyday in those first 21 days but if you can get through that, it will turn into a habit and will be much easier.
Start with just one habit. Once that comes easy, then add another habit to work on. It's the simplest and most effective way to change the things you want to change!