Aisle seat with open middle is the most coveted seat for me. My strategy for this is to take the aisle 1-3 rows behind the exit rows then lean into the center to make the space look as cramped as possible.
By time you get to the end of the C group, you generally have two batches of folks. Those that will take the first available middle seat in the font third of the cabin to get off quicker...then those that will keep hunting for a better seat and continue to the back third as they lower their expectations leaving the middle third of the cabin where most of the empty middle seats wind up.
I never take the exit rows. I always wind up with the biggest dude in the C group plunking down right there in the middle seat.
Not a fool proof plan and FAs always look at me like I am crazy for passing up a wide open exit row but more times then not I wind up with an open middle on mostly full flights.