My two tips for how to keep the adjacent seat empty on normal flights: 1. If you book when there are still many empty seats, choose a window/aisle seat near the back of the plane. Those middle seats are usually the last to be filled. 2. If you're traveling in a group of 2 and there are 3 seats per section, choose the window and aisle of an empty section (preferably near the back of the plane). Chances are good that i…
YMMV (and I hope it does)!