never anything 'diet', never anything 'low-fat' (that means high sugar), as much veg as you like, lots of complex carbs (wholemeal bread, pasta, rice etc), no supplements, no fads. About 2000 calories a day and move for half an hour a day to maintain weight. Obviously go easy on the sweets, cakes, biscuits. Fizzy canned drinks are only suitable as toilet cleaner. Booze is full of sugar so apart from the other effects, it will make you fat.
if you are a bit fat, move more - realistic weight loss rate is 1lb a week or less.
it's simple. The above also won't make anyone any money which is why the diet peddlers don't talk about it.