The microorganisms that break down organic material in your soil will happily do the same job in a pile of fallen leaves and plant trimmings. Your role as a composter is to provide the conditions for nature's crew of decomposers—the bacteria, fungi, and bigger creatures such as sow bugs and worms—to go to work. Browns, Greens, Air and Water are the "big four" that will keep every compost pile happy.
Composting is as easy as 1,2,3:
1. Chop materials to help them break down more quickly.
2. Mix "browns" (dry, woody materials) with "greens" (moist, green materials).
3. Maintain air & water balance by keeping compost as moist as a wrung-out sponge.