In any sequential situation, reason forward but decide backward: start from the final move, determine what each player will choose there, and use that to solve the move before it, working back to the present. Your best current choice depends not on where you are but on anticipating every rational response that will follow.
A threat or promise only works if the other side believes you will actually carry it out, which often means visibly destroying your own escape routes so that compliance becomes your only rational choice. Burning a bridge behind an advancing army, or signing an irreversible contract, can strengthen your position precisely because it takes a tempting option off your own table.
If one option gives you a better outcome than another no matter what your opponents do, you should simply play it without trying to forecast their behavior. The rule is to look first for a strategy that dominates all your alternatives; only when none exists must you reason about what others will choose.
In situations where any fixed pattern can be exploited by an opponent, the best play is to randomize across your options with calculated probabilities rather than choose one reliably. A tennis server or penalty-taker who becomes predictable loses the advantage, so deliberate unpredictability is itself the optimal strategy.
When each party acts in its own narrow interest, the collective result can leave all of them worse off than if they had coordinated, as when competitors cut prices into mutual loss or everyone overuses a shared resource. The trap persists because defecting is each individual's best response regardless of what others do, so good outcomes require changing the game's structure rather than appealing to goodwill.
Rather than optimizing within a fixed situation, a skilled player alters the rules, information, or incentives others face before they act, using commitments, threats, and promises to shape their choices in advance. The leverage lies in moving first to constrain the game itself, not in playing a given game well.