You can square up a wall before raising it by measuring from opposite corners. Assuming that both the top and bottom plates are equal in length, and that both ends are the same, the wall is square when the diagonal measurements are equal. Adjust the wall as necessary, then keep it square with sheathing or with diagonal braces before raising it.
If the microorganisms have more surface area to feed on, the materials will break down faster. Chopping your garden debris with a machete, or using a chipper, shredder, or lawnmower to shred materials will help them decompose faster.