Use Google to search for yearbooks for the military. Ancestry has some online for school yearbooks. Try to find the name of the yearbook or in the case of the military, try the military unit or brigade. Don't forget to cite the source.
As you research your ancestor's military history, pay attention to the specials on websites like Ancestry, Fold3, and My Heritage that run around Veteran's Day and Memorial Day. Take advantage of them. In the last week, I found two books on the battalion that my grand uncle served with. They are a wonderful additon to the material that I have to assist me in writing his story.
No matter how many times I attend conferences, I always learn something. Today I attended two presentations about searching for military members of my family. I learned about documents available other than draft registration cards.