Frequent travellers know about extra leg room in seats near exit. But other seats in economy class also have different seat pitch. Is that additional inch makes such big difference? Oh yeh! Especially then you are crossing Pacific ocean and spending 12 hours in the air. Every year I fly at least once around the World and just before my last such trip I found very helpful site SeatGuru. Of course you can not be 100% guarantied to get seat you want, as airlines can change aircraft for particular flight, but it worked for me and I was lucky to get better seats especially for longer flights.
On the left there is example of color-coded seat map to help identify superior and substandard seats.
But it is not only about extra legroom, there you can find detailed seat map with comments about seats with limited recline, reduced legroom, misaligned windows, in-seat power port locations, lavatories, exit rows and etc.