When you're working with old photos, or with new photos that you would like to look old,
vignetting is often the trick that makes the difference. It gives that sort of cameo look as the portrait subject comes forward and the background fades to nothing. Here's an easy way to do it.
Draw an elliptical selection marquee around the portrait subject. Invert the selection so that the background is selected. Feather the selection by whatever amount looks right (choose Select