the Hedge-Wizard's Commission (the Death-god of Akrahmur Book 1)

In the lands of Akrahmur in the far East, an ancient evil has been building its careful plans for centuries while the kingdoms of men grow weak and diminish. A vast and terrible horde of men and of unnatural creatures prepares to sweep down from the icy mountains into the fertile kingdoms below. On the eve of their destruction, men go on as they always have, oblivious to their doom. Sleepy oxen drag plows across rows of wheat, world-weary farmers whisking long sticks above their great shaggy heads.
And in the Woldenwood forest, far from the great cities of the world, the boy Finnan embarks upon his apprenticeship to a strange and mercurial old Hedge-Wizard.
Finnan has no particular importance to the world. He's not a lost prince or a great warrior. He's only a poor villager who quickly finds that he has very little talent for magic. But in spite of that, he is soon to be swept into the very heart of a war among men, wizards and monsters to determine the fate of all mankind.
If he could only learn a useful spell or two, perhaps he'd have a fighting chance.