pinniped

More to the point of the OP, on most airlines there isn't a very reliable way to avoid it. It sounds like you're thinking "If my flight is 95% full, how do I select a row where my likelihood of an empty middle is greatest?"

I imagine most airline boards here have their theories. Southwest regulars have their favorite rows to head for in hopes of the last empty middle seat. In my UA years, I always felt like my chances were greatest in the last non-exit E+ row. On US, there are a couple of aircraft types where there are seats that elites can book adjacent to two seats that no one can book without paying extra...but paying extra for one of those seats could be a gamble that backfires at a cost of some real cash.

These days, if we're in a 3x3 or a 3x3x3, we go aisle-aisle. Everything's 100% full anyway, so we figure two aisles beats an aisle and a middle.

My personal opinion on the practice of booking window-aisle: I think it's fair game to try it, but I think it's pretty poor etiquette to not offer to swap with Mr. Middle when the flight is 100% full. I was in that situation once - in the middle - and it was an unpleasant flight for all three of us. I too had to use a newspaper as my defense...