The goal of a prepper is survival, not to be a police officer, soldier, or partisan. However, as happened in Egypt during its "Arab Spring," and in Haiti following the earthquake there, and in other situations where rule of law has disappeared, neighborhoods and communities have had to act to defend themselves against criminals and looters. Thus, it behooves preppers to learn some basic small unit tactics.
One of the conundrums, though, is that preppers do not have access to military weapons. Tactics must be adapted for using civilian weapons. Consequently, you may find this article from Warrior Talk News on the tactical use of shotguns in an ambush to be interesting and potentially useful.