I am small-framed and slim; always have been. Don't have any scales and never weigh myself, but I'm 5'5 and a size 6. I have two kids, and I am the same shape as I was when I was in my twenties. (I'm 50 now). I eat what I like and could do with cutting back on sugary stuff and doing some exercise (I'm not at all toned, look far better dressed).
The only time in my life I ever put on weight - don't know how much but I was noticeably rounder/heavier - was when I lived in the States for a few years. Portions were massive; I couldn't manage them at first, but slowly I got used to them and ate like everyone else. After about a year, dh and I started taking sandwiches to work instead of going out with everyone else, and I just started ordering less if we ate out in the evening (a starter instead of a main course, for example, as even the starters were enormous). Otherwise no restrictions - within a few months I was back to the way I was.
Otherwise, as I say, I sort of eat everything in moderation, I guess. I always have a glass or two of wine if we eat out (which we do quite a lot) but we rarely drink at home. I try to make sure we all eat a lot of vegetables and salads for health reasons, but otherwise we eat across the full healthy-junk spectrum.
I don't give it a lot of thought - although I wouldn't mind firming up my flabby bits, am essentially too lazy - and that's probably half the battle. My advice to anyone would be to start with portion size. You don't need to eat bird portions, but cut it down by a third or whatever. You'll soon get used to it.
(And I guess treat each glass of wine like a mars bar - which calorie-wise I think it is? - and maybe ease back on those too)