I tend not to order something I think I mightn't finish.
If I'm not that hungry I'll skip the starter and just have the main course.
If I'm full after the main course I won't have dessert.
I suppose I'm pretty disciplined that way even though I do really love my food.
I don't think it's as bad here in the UK as it is in America though as the portions there are enormous.
Heh heh... that reminds me of a story when we went to the Ponderosa Steak House the first time we were in America.
For those that aren't familar with it it's an all you can eat buffet.
Anyway my wife and I had had a plateful of chicken wings salad and other tasty nibblers, then finished our main courses and we both had what I would class as a large steak and chips (french fries) dinner.
Both of us were full and when the waitress came over she told us about the desserts.
I said to her 'No thanks, actually we're both pretty full'.
She looked at me in shock, as if I'd three heads, and said 'Are you guys not having DESSERT?!!!'
Her reaction was so noticeable it was genuinely as if no one had ever said that to her before in her entire life and I couldn't help thinking 'Wow is it really that rare that the people that come there don't eat massive meals?'
I don't know the answer to that question BTW but having seen the sizes of the helpings in most US restaurants I couldn't help wondering if that was true.