The single most biggest change (can I say it like that?) is eliminating sugar outside of fruits. I even cut out the main staple in my diet, chocolate! Only eat chicken, fish, vegies and fruit. Bread comes from bread store and is very different from what is in the grocery store. Have pasta one day of the week, if that. Seems my diet is more Atkins than anything.
Vegan diets don't work for my body, tried it in my 20's and it just didn't work for me. Left me lethargic and tired for 1.5 years. As soon as I added meat into the diet, the game changed.