Coming up with poses is the fun part. For this next set we are doing an "advancing" set. Marching, jogging, and firing on the move. We've got just one prone figure planned with this set, and it will most likely be a firing pose as well.
The way I like to plan poses is to use real people, and let them find a comfortable pose or position. Using flesh and blood models cuts down on physically impossible and awkward stances. I get a model into uniform, and have them go through the firing motions, or charge a few steps, or just start moving around randomly, all the while I'm snapping pictures. Afterwards I go through all the pictures, find something I like, and then off we go to the sculptor. The sculptor will usually throw in a few tweaks, based on molding capabilities.
Some notes about the photo above: you may notice that it's the same person that posed for the "sitting, firing" Confederate. It's the same hat as well. I just use these pictures as pose guides, not so much uniform guides. Each of the Federal figures will be equipped with a Springfield rifle (not the Enfield pictured above), proper leathers (not late war leathers as seen on most reenactors), and a Hardee hat either telescoped, creased, or left plain (a couple might have a civilian slouch, and of course one does have a kepi with an upturned bill).
I'm considering doing more than six poses for the federals, depending on how things go. I'll let you know more as I know more.