During the Franco-Prussian War, what infantry tactics did the North German Confederation/German Empire use? (i.e. infantry formation, placement, where/how/when to shoot, etc).

More can always be said on the matter (the post-Napoleonic, pre-WWI European wars get comparatively little coverage compared to their leftpondian contemporary the ACW); for the meantime, we do have some previous posts on the matter.

The now-deleted u/elos_ has this excellent overview on the Austro-Prussian and Franco-Prussian Wars;
u/Superplaner provides, with pictures, a rundown of Prussian tactics.