^^^ that works well for those with smaller appetites
Firstly, it depends on what type of restaurant. If it is a chain restaurant then I'll normally just peruse the menu, find something I like, fit it in to my daily cals. This may mean going a bit lighter on cals during the day.
If it's a "fancy" restaurant that I rarely go to, I'll normally just get something that I wouldn't usually cook (or be able to cook) myself. One higher calorie meal won't make you fat, just like one lower calorie meal won't make you shredded.
During comp prep, I only went to fast food places as can get nutritional info easily. Fancy chef's give no fark for macros/cals just flavour.