Jamie oliver's books are all good for this but his new one - Healthy Eating or whatever it's called - has some great ideas. HIs meals are usually much more balanced.
We eat pretty healthily. For me, meal planning really helps with this. I find it quite boring, but it means I can really think ahead about my schedule and whether we've got enough variety in for that week.
We do also try for 30+ plant based foods a week which helps with mindset of ensuring we're getting that variety.
I think if you're starting out, I'd suggest starting relatively small. Think about 2-3 evening meals a week you can really prioritise getting diversity and nutrition. Burrito bowls or tacos are a great choice for us for this because usually it's some kind o fproten, rice/tacos, then I aim for some kind of salsa using fruit and veg and then an additional side with veggies. Last night was a salsa with red onion, tomato and charred corn, with avocado slices on the side. Next week we're doing pineapple, avocado and onion salsa and I'll probably do some chopped tomatoes or lettuce alongside.
Ditto, for lunch, I try to make sure I'm eating soup or a salad at least a few times a week. Or instead of a quick cheese sandwich, I'll make peanut butter on toast with banana or an open tuna sandwich with some lettuce/avocado/pickles on the side. Not necessarily low fat, but more nutritious.
I make home made granola most weeks for eating at breakfast with yoghurt. I do have a habit of just having a slice of toast with butter and jam though or, if I'm in the office, a pastry! I'm trying to do that less often! I've often done crackers with cream cheese and avocado for breakfast too, or boiled eggs on toast is a regular one here if I'm eating a bit later.