Picking a good seat can be detrimental to a good flight experience, it can make a great airline appear awful when in reality it was your specific seat to cause most of your complaints.
Seat position is extremely important in having a good experience, especially during long haul flights. Minuscule things that would not bother short haul flights could become a much bigger issue. Aircraft type is also important and one must be aware on what they are flying as some flights will have updated cabins and others wont.
This is my Personal checklist I go through before selecting my seats.
1- What Airline am I Flying?
2- Which Aircraft am I Flying?
3- Is there an opportunity to sight see during takeoff/landing?
4- Check flight information via https://flightaware.com/
Once I gather this information, I do quick research on https://seatguru.com/
I input flight number and date I’m flying and I make sure to match the results to the actual aircraft I’m flying as sometimes this can be different from the information SeatGuru displays.
The seats are reviewed by fliers and some even include pictures. You can see the information that way you never miss a window seat, or be bothered by the lavatories again!