i know it's a cliche but it really depends on where you're eating, and what you eat at home.
I don't know about you but if I'm cooking at home, I'm not necessarily measuing everything by the gram. Sure, I know what's in it, but not to the same level as a ready meal where you can say 'right, that's 47.5g of carbs on my plate here'. So to some extent, my carb counting is guesstimating - it's all about learning to eyeball your food and make quick judgements.
Same principle with restaurant food - you take a look at it, have a rough guess based on the description what's in it, and dose accordingly. I suppose it would be easier to have carb counts on the menu but then that would make me wonder if it's come out of a box rather than being freshly cooked, and would end up making the menu look very dull!
If it's a chain restaurant thoughl, often you can get nutrition information online which can really help.
What I find helps more than anything is experience - and cooking yourself. For instance, a lot of Chinese food tends to raise blood sugar more than people expect and it's not until you actually start cooking it for yourself from scratch that you realise just how much cornflour is used - it's in most sauces and every meat is dusted with it because it helps with moisture retention. You could put it on a menu that cornflour is used, but I think it wouldn't really register with most people until they actually see for themselves what it means.
I'll be honest though, I've never really had a huge problem eating out. I work the principle that whatever bolus I think I need, probably add another 30% and even if it doesn't work out, I only eat out maybe twice a month anyway so it's not as if it has a dramatic effect on my overall control. Plus I tend to make choices that I know are low in carbs anyway - that way you're less likely to over or underestimate the carbs in the meal as you're dealing with smaller numbers. I'm a meat person so generally my order is a massive lump of dead animal with some salad for decoration, so often it's only any sauces/marinades I have to factor in.