I agree with a PP that it should be a way of life from the beginning. It has been for us, and even though DD will sometimes refuse to eat a certain veggie, other times she will eat it right away. She is getting better now that she's a little older (2), but when she was 1 I remember sometimes having a hard time with certain veggies, and thats when I started hiding them. I think that its important to both hide them and serve them, because then they get used to seeing them and the texture and taste of plain veggies vs hidden ones.
I think its also important not to overdo it on sweets and junk food, because they get used to the taste of those things which unfortunatly most of them prefer, and then they wont eat the healthy things that are not super sweet or processed. I'm saying this from experience- watching friends feed their kids candy and junk from the time they first start eating and then wonder why they throw a fit about vegetables when they offer them occasionally.
It has definitely been our way of life from the beginning. I eat about 6-8 servings of vegetables and they are available every meal. We are also gardeners and we grow a lot of our own veggies. Still they don't want to eat so many of them. There are random times that they do.