I recently had to resize 48 images of various types and formats into 20×40 images. I am not an expert in Photoshop and started manually making changes. I noticed the Batch action available in the file menu (when saving the 4th file for those curious), and after a quick google search found this GREAT article.
Follow it explicitly (except don’t SAVE the file choose DONE. Saving the file in the custom action results in every file in the batch being saved as that file – and subsequently rewriting every previous effort).
Enjoy the added efficiency, and like my friend David used to say – get a sandwich while it works…