For most people eating moderately at regular intervals is the key to good health. Mixing and matching your food types, varying the color of your vegetables and avoiding processed foods (pre-cooked, pureed, mashed, imitation sugars and preservatives).
For anyone who finds it difficult to give up their favorite foods a keen method of putting your passions to work for you is to change from "x" number of meals per day at your usual quantities to eating half as much (of the same foods) at each sitting but doing that twice as often.
This will result in you loosing weight. It's like magic but it's actually just physiology. We burn calories by eating and digesting food, the trick is to break down how much the body has to work on at each sitting.
So if I normally eat a steak, mashed potato, peas and a large drink I should eat half that steak, half the potato and as many fewer peas - even half the drink (drinking with a meal interferes with digestion anyway but that's a different subject) then eat the other half at least 2 hours later.
If we wait too long between meals (the feast and famine routine) our bodies go into starvation mode and store more fat. If I wait too long, I get "hunger headaches" that risk becoming migraines. Not fun. Like only drinking water once a day. Our bodies are machines, without proper maintenance we risk damaging it unnecessarily.
If we eat fake sugars our bodies still react to the stimulation as sugar but without having anything to break down there is nothing gained by it. Depriving our bodies nutrition is rarely the answer but since each person is different, you should always consult a dietician first and let your Doctor know what you are up to.
If you can't brush and floss after every meal, have some toothpicks on hand. Get out the visible things, stimulate the gum line and swish away any residue. The extra stimulation of the saliva glands (without adding more food/soda/coffee/tea/milk to the mix) helps tremendously to prevent problems in the future.
So to be more direct, it's better to eat 6 half sized meals if you're trying to lose weight. It's better to eat regular amounts at regular intervals if you're maintaining. Eat large breakfasts and small, easy to digest dinners for a less troubled nights sleep and waking up more refreshed. Avoid eating only one meal a day unless you're trying to store fat and play jungle gym with your insulin levels.
Other tips? Milk is for cows, as adults there are other methods to gain the perceived benefits that milk provides. Ask a dietician for some examples. Whether or not you drink milk, you should have your Vitamin D levels checked every now and then.
Giving up anything with caffeine, tannin (teas), alcohol (even wine) will also improve your health. If you feel that these substances give you specific benefits that outweigh the damage, consider finding another (healthier) source for those benefits. I could smoke to improve my short term memory but the lung cancer isn't a fair trade for that one benefit in my experience.
Don't take your health for granted either. Everyone's body is different but general guidelines (such as this answer) are a good place to start. Whenever considering any changes to your health, consult your Doctor and get regular checkups. The ability to look in the mirror and assess your health is about as accurate as looking at a side of beef and determining it's fit for human consumption. (Although don't tell the Government that, that's actually how they test for Grade A beef if I recall.)
When in doubt, eat the best food available to your region. So it follows that as you travel or the seasons change, what is "best" will necessarily be different also. Do your best, enjoy variety, don't torture yourself. Bon appetit!