So, this weekend, one thing that we worked on was the drill for the civil war skirmisher. When most of us think of a skirmisher, we think of some guy hiding behind a tree, sneakily trying to catch some hits on the other side. During the Civil War, however, units would actually be sent forward in staggered line, alternately shooting (when in front) and loading (when in the rear). They would take cover behind trees or rocks if possible, though if those options weren't available, they would crouch or splay out on their stomachs to avoid enemy fire. An excellent history of the skirmish can be found here.
Below, however, I have placed an excellent drill, made by the 10th Pennsylvania Reserve Volunteers, Co. G. Follow it, and you can see the basics of a skirmish drill in all three steps: deployment, advancing, and retreat. As a note, skrimishers would retreat, usually not because they had lost so many men, but because the rest of the army was coming up from the rear in support.