The biggest part of the joke is the punch line, so the biggest part of a book should be the punch line, the ending. People don't read a book to get to the middle, they read a book to get to the end and hope that the ending justifies all the time they spent reading it. So what I do is, I get my ending and, knowing what my ending is going to be, then I write to the end and have the fun of knowing where I'm going but not how I'm going to get there.
Once you have decided that Othello kills his wife and then himself, the rest of the play is getting to that point by the most efficient and convincing route.
Yet first lines can be fun, and fun is more important than importance. Here are my two favourites that I doubt you know.
The sun shone, having no alternative, on the nothing new.
- Murphy by Samuel Beckett
I was an infinitely hot and dense dot.
- My Cousin My Gastroenterologist by Mark Leyner
You are invited, dear reader, to post the best first line that I haven't heard of in the comments below. But no universally acknowledged truths called Ishmael striking thirteen.
Oh, and: An Irishman, a rabbi and a flamingo walk into a bar and the barman asks "Is this some kind of bloody joke?"