Cutting up a design with the “Copy Merged” feature is fairly easy:
ensure that the layers are shown or hidden as needed; draw a Marquee
selection around the element; choose Edit → Copy Merged, and then File →
New; hit Return; and then “Paste.” The result is a new document with
your item isolated, trimmed to the absolute smallest size possible.
From here, all you need to do is save the image using “Save As” or “Save for Web & Devices.”
Rinse and repeat for every image needed for the app or website. The
technique is simple and quick, but repetitive; and if you ever need to
export the images again, you’ll have to start from scratch.
This seems to be the most common method and, for some designers, the
only method, which is a shame, because better techniques exist.
You could create an action that triggers the “Copy Merged,” “New,”
“Paste” process — a small time-saver, but ultimately not much of an
improvement to the workflow.