All's fair in love and war
A Deadly Distraction
Not sure if this counts as a ‘trick’, but Napoleon prior to the Battle of Marengo.
Not only did he cross the Alps with his entire army (a completely unexpected move), but once across, the Austrians thought Napoleon would move to Genoa in order to relieve the siege of that city. Thousands were dying of starvation, and French general Massena desperately called for Napoleon’s aid.
Napoleon, in a ruthless and surprising move, ignored the calls for help and instead moved to attack the main portion of the Austrian army, eventually winning the Battle of Marengo.
Massena surrendered Genoa and it would be years before he eventually forgave Napoleon for abandoning him (and it would be years before Napoleon forgave Massena for surrendering). (lebeast)
Scorched Earth Politics
The Russians and their use of a scorched Earth policy. I can’t think of a better way to flip off your invaders than ruining all your own shit so when they do take it, it’s worthless. Not only that, but the land itself is just too damn cold. So go ahead, take the land. You will just freeze to death. Congratulations. (MonkeyXing)
Into the Cannons
Not so dirty, but Turks had the Turan tactic.
The army would formate into a crescent, with the arms of the crescent being the armored, strong divisions and middle front being the fastest divisions and middle back being the highest firepower(cannons). They’d start the battle lined up and charge, then the fast middle front guys would start retreating to the lines behind the middle back(the cannons). The arms of the crescent would hold firm because they were the armored part. The enemy would think they were retreating completely(because it looks like they are losing their s**t and also their formation)and would chase after them only to be met with the cannons and to be encircled by the crescent’s arms. It was a slaughter of the enemy after that. (ArefArif9)