Answer:
I'm answering this based on my knowledge about a research paper I am writing about on Alexander the Great (i assume that is to whom you are referring).
One way he prepared Alexander would be, indirectly, through the Macedonian Army; basically, he changed their formation and also introduced some new weapons.
It is also probably helpful to read the following:
Philip II, the king of Macedon whose assassination in mysterious circumstances back in 336 had originally brought Alexander to the throne, was a man who had proved himself the most dangerous enemy that Athens had ever faced. Inheriting a kingdom on the verge of implosion, Philip had left it a superpower. The monarchy itself had been centralised, Greece subordinated, and the Macedonian army transformed into a lethal and incomparable killing machine. Here was the inheritance which had enabled Alexander to make his conquest of the world. Demosthenes, who had spent his whole career in a fruitless attempt to oppose Philip's rise to supremacy, appreciated that better than anyone. It needed no god to explain Alexander. Philip was more than explanation.
In conclusion, he helped him by leaving behind tools which aided Alexander in succeeding in his future endeavors.
I'm sorry this is not too organized but I am still in the planning stages. Hope I was a bit of help! :D