I have been on crash diets before (cabbage soup diet was harsh but worked), but I have never been able to dedicate myself to a proper, moderate diet, I like food too much and lack persistence. I am pretty much on the go all day, so I am fortunate enough not to have to worry about weight. I ensure I have more veg than meat and potatoes, and having never had a sweet tooth am not particularly fussed about pud.
I find, and avoid, certain foods that trouble me. Bread and potato bloat me and make me feel sluggish shortly after.
A few tips, though:
Tin tuna - buy in spring water, not brine
Pork chop - lubbly jubbly, but trim the rind off (i'll eat that, it's the best part!)
Gravy - a no no, especially if you add the fat from the meat.
In my experience, if you are a snacker, you are best off eating raisins (high in sugar) than crisps (higher in fat).