If I know it is not a full flight, I look for the least desirable person in the window seat. I then take the aisle. Old lady coughing with a mask on? Count me in! Obese person in window? Count me in!
I employ the opposite strategy on a full flight if I know I will have someone in the middle. I don't need a fat person squishing them over into my area.
Also, if you can find a COS, you have hit the jackpot. No one can take that middle seat.