• New double- or triple-pane windows are best, but you can also add storm windows, interior sliders, or even a big pane to seal up the window permanently. You want gaskets, too: felt for rattly old sashes, vinyl for casements.
• You can upholster walls with cotton wadding covered with anything from chintz to flannel. For draperies, go with heavy velvet or wool. If I were in a third-floor walk-up, I’d get an area rug with a pad.
• If you’re remodeling, you can put in fiberglass batting between the studs. Also, use metal clips between the drywall and studs for an extra layer of air. If your neighbor is clomping around upstairs, the only thing you can do is ask them to take off their shoes.