Va'era 

וארא

The order of the plagues was not random; rather, it was calculated based on shrewd military tactics. There was also an element of punishment administered measure for measure to Egypt. 

Our Sages, of blessed memory, said: The Holy One, blessed be He, brought the plagues upon the Egyptians in accordance with the tactics of kings. In the case of a human king, when one of the states under his rule rebels against him, he sends legions against it and surrounds it. First he dams their aqueduct. If they relent, fine; if not, he brings producers of loud noise to harass them. If they relent, fine; if not, he shoots arrows at them. If they relent, fine; if not, he brings barbarians to attack them. If they relent, fine; if not, he brings chaos upon them. If they relent, fine; if not, he throws naphtha, a flammable fuel, upon them. If they relent, fine; if not, he casts catapult stones upon them. If they relent, fine; if not, he sets masses of soldiers against them. If they relent, fine; if not, he incarcerates them in prison. If they relent, fine; if not, he kills the greatest among them. So too, the Holy One, blessed be He, came against Egypt with the tactics of kings. First He dammed their aqueduct by turning their water into blood…The Egyptians did not relent. He brought producers of loud noise against them – these are the frogs. Rabbi Yosei bar Hanina said: The frogs’ croaking was more difficult for the Egyptians than the damage they caused. The Egyptians did not relent. He shot arrows at them – these are the lice, which would penetrate the bodies of the Egyptians like arrows. The Egyptians did not relent. He brought barbarians against them – this is the swarm. The Egyptians did not relent. He brought chaos upon them – this is the pestilence, which killed their livestock. The Egyptians did not relent. He threw naphtha upon them – this is the rash. The Egyptians did not relent. He cast catapult stones upon them – this is the hail. The Egyptians did not relent. He set the masses against them – this is the locusts. The Egyptians did not relent. He incarcerated them in prison – this is darkness. The Egyptians did not relent. He killed the greatest among them. Everything that the Egyptians planned for the Israelites, the Holy One, blessed be He, brought upon the Egyptians themselves. The Egyptians thought the Israelites would be their water drawers. Therefore: “He turned their rivers into blood” (Psalms 78:44). The Egyptians thought the Israelites would carry their merchandise. Therefore, God brought frogs upon them, which would destroy the merchandise. The Egyptians thought the Israelites would till the land for them. Therefore, God filled the land with crawling lice. The Egyptians thought the Israelites would carry them like a caregiver. Therefore, God sent among them the swarm: lions, wolves, tigers, bears, and vultures. If the Egyptian had five children and gave them to the Israelite to take out to the street, a lion would come and take one, a wolf would take one, a bear would take one, a leopard would take one, and a vulture would take one. The Egyptians thought the Israelites would herd their livestock. Therefore, God sent pestilence among them…. The Egyptians thought the Israelites would boil water for them. Therefore, God sent a rash among them. The Egyptians thought to stone the Israelites with stones. Therefore, God brought hail upon them. The Egyptians thought the Israelites would care for their vineyards. Therefore, God brought upon them locusts that consumed their trees: “They consumed all the vegetation of the land and all the fruit of the trees” (Exodus 10:15). The Egyptians thought to incarcerate the Israelites in prison. Therefore, God brought darkness upon them. The Egyptians thought to kill the Israelites. Therefore: “The Lord smote every firstborn” (12:29). The Egyptians thought to drown the Israelites in water. Therefore: “He hurled Pharaoh and his army into the Red Sea” (Psalms 136:15). <source>(<i>Tanĥuma</i>, <i>Bo</i>) </source>