The "advance and retreat" part is really important. Don't assume that a retreat means defeat. Don't assume that an advance means a conflict is over. Evaluate it in its entirety, not only based on the current step.
Even when we are not talking about explicit hot war, expect action and reaction. Think about and observe what actions cause what reactions in a certain context and why. Liberation forces must be prepared to suffer setbacks and work through the problems that arise. Likewise, they must be prepared to seize on strategic gains and build upon them, without overextending or growing arrogant in their current position. The answers to where the lines are will come from experience, study, and adjustment in context because the landscape is often shifting and contextual; there is not a universal, static answer key.