I'd start with homecooking as often as you can, and if you can't, go for less processed food. The more natural the better.

I find it helps to make at least half a meal either veggies or fruit. My family loves meat and potatoes/pasta so, I usually make the other half of the meal (at most) a combo of the two. Complex carbs like sweet potatoes and whole wheat pasta are better than simple startchy ones like white potatoes and pasta. We encourage our Scouts to "eat a rainbow" every day. Them more colourful your meals the better - green veg + orange veg + red veg etc.

Slip in veggies wherever you can. I have to hide things like carrots from myself sometimes. Grate some sweet potatoes or carrots into your meatloaf, use tomato sauce instead of cream and snack on fruit and veggies.

Also, remember that many people confuse thirst for hunger, so be sure to drink lots of water.