Finding the best plane seat in economy just requires an understanding of how airplanes are configured. You should also plan ahead to optimize your selection and ensure you get it. Airlines configure seating to their own specifications therefore this will vary by airline. Seat pitch is the distance between seats. Seat pitch varies by airline and aircraft but can be less than 30cm. The style of seat varies also and the airlines are constantly working on innovations to improve the “sit-ability” of the seats on the flight. The best idea is to try to check in early. Try for an exit row where the seat pitch is wider to allow passengers to exit quickly in case of an emergency. Some airlines charge extra for these rows of seats. But it may be worth it especially if you are 180cm tall. If the airline charges extra for these seats, you will be able to book this seat at the time of booking or when you are completing online check in.
Some people like the window because they can curl up against it and sleep better. The downside of the window seat on long haul flights is that you will be needing to get past 2 or 3 people to get up to stretch your legs or use the bathroom. The aisle seat on the other hand gives you easy access to the aisle. It may not be as good for sleeping and there is the risk of being disturbed by passing food and beverage trolleys however.
The undisputed worst seats are those in the middle at the back where turbulence creates the greatest impact. However it is usually cooler down the back if you struggle with the temperature on airplanes.
Seat selection tools are available Click here for some more on seat selection tools.