I'm 1.8m (6ft) and 65kg (140lbs) and I don't look very good. But then, I'm not really trying at all.
But common sense tells me:
a) You have to eat much more than you're used to, but don't eat crap (pizza or McDonalds is not food - it's crap).
b) You actually have to move a lot. Which is consistent with exercise advice from previous posters. And you need to move not merely to build up muscle (although that won't hurt), but primarily to
make yourself hungry! And this I can vouch wholeheartedly: After significant physical effort (which happens to me on occasion
), like a mountain trek, I eat much more than usually.
If you keep sitting at your computer (or books, or toy train obsession) and keep feeding yourself tons of noodles, you'll just turn from a very thin person into a thin person with an ugly bum and belly.
I'm tellin' ya...eat as much as you can and drink a gallon of whole milk a day. And lift.
<-- A+++++. I'm doing Starting Strength's 3x5 workout.
. 6' 144.5lb and 6' 160lb, respectively.