Where you sit while flying, especially in tourist class, can make a big difference to your comfort during a long journey.
When you travel tourist class and you want leg room, remember that the seats near the emergency exits do not have seats immediately in front of them. Another advantage is that there is no passenger right in front of you to lean back his seat at inconvenient times, usually when he or she has finished eating. Many passengers are completely selfish and inconsiderate. Besides, if necessary, you could be first out in an emergency!
A disadvantage, however, is that you can't put anything under the seat in front of you. Nor should you put it under your own seat, which is for the benefit of the passenger sitting behind you. However, if you are whiny, stubborn and truculent, you may get away with it!
Many years ago now, I was on a flight to Iceland and the lady in front of me, an apparently chic and sophisticated French woman, had an emergency exit seat. Of course, I put my own convenience bag under her seat, as the signs said that I should. As the woman could not put her bag under her own seat, she put it on the floor in front of her. Of course, the steward, would not permit this, for reasons of safety, and he rightly insisted that the woman allow him to place the bag in the locker above. She absolutely refused. The steward then asked me if I would relinquish my right to put my own convenience bag under her seat. I reluctantly agreed and spent the rest of the flight at some inconvenience. The moral of the story is that you can have it all if you are selfish, rude and nasty enough (sorry for being a little bitter).
You must also choose, if they are available when you reserve your seat, whether to have a window seat or a seat next to the aisle. Personally, I like to look out of the window while flying. The down side is that I have to squeeze past other passengers to reach the aisle if I need to have a pee. On the other hand, if I had an aisle seat, other passengers would have to squeeze past me when they needed to pee.
It could be worse. In the movie Bullet to Beijing, the heroes have to fly in an extremely crowded 'plane and one of them has to sit in the toilet cubicle, along with another passenger. He objected when his companion informed him where he would be spending his journey but if I were on a crowded plane in which the toilet was just another seat, that is where I would like to be. I don't like long queues or blocked aisles. Come to think of it, the hero in the toilet did find some advantage in his placement, after all.