Let your plans be dark and as impenetrable as night, and when you move, fall like a thunderbolt.

故兵以诈立，以利动，以分合为变者也，故其疾如风，其徐如林，侵掠如火，不动如山，难知如阴，动如雷霆。掠乡分众，廓地分利，悬权而动，先知迂直之计者胜，此军争之法也。
全文
In war, practice dissimulation, and you will succeed. Whether to concentrate or to divide your troops, must be decided by circumstances. Let your rapidity be that of the wind, your compactness that of the forest. In raiding and plundering be like fire, is immovability like a mountain. Let your plans be dark and impenetrable as night, and when you move, fall like a thunderbolt. When you plunder a countryside, let the spoil be divided amongst your men; when you capture new territory, cut it up into allotments for the benefit of the soldiery. Ponder and deliberate before you make a move. He will conquer who has learnt the artifice of deviation. Such is the art of maneuvering.