Portions are always tricky to get used to since restaurant portions are, usually, significantly larger than an average meal, that's why if you do eat at restaurants you should eat half or less there and take the other stuff home. (That's what I do at least.)
Also important with a diet is to not quit eating certain foods cold-turkey. The problem with this is that if you do happen across a situation where you have to eat your problem foods, you're likely to overindulge. The goal, rather, is to wean yourself off of them. Eat a peanut butter sandwich once a week, then once every other week, then once a month, then once every other month, then hopefully by then (or even before?) you'll have found a substitute that is better for you. (Of course, peanut butter and bread isn't terribly bad for you since there's a lot of protein and good fat in peanut butter.)
I can't really give you advice on green tea since I personally prefer sweetened iced tea, but I can recommend to you Honest Tea brand teas. Most of their teas are either unsweetened are very lightly (like 6g of sugar per bottle rather than the 20+ of other brands) and are organic. Or you could just brew your tea yourself if you really wanted to.