1. Finish editing all of your 12 rule of thirds photos. See Friday's entry for some extra tips on editing.

2. Rename your photos as such: (you can do this pretty quickly at the end, after you've completed all your edits)
          portrait1.jpg, portrait2.jpg, portrait3.jpg
          landscape1.jpg, landscape2.jpg, landscape3.jpg
          object1.jpg, object2.jpg, object3.jpg
          whatever1.jpg, whatever2.jpg, whatever3.jpg

3. Run a contact sheet containing all 12 of your images by clicking File--> Automate--> Contact sheet II. Select what files you want in the 1st section of the contact sheet menu. Leave the middle section alone! Change the bottom section where it says "columns" and "rows". You want 3 columns and 4 rows (because you have 12 pictures, and 3 x 4 = 12)

4. Name your contact sheet LASTNAME_FIRSTNAME_thirds.jpg

Here is a finished example containing some of my best rule of thirds photos by students: