If it is too small, it is difficult to maintain adequate temperatures for rapid decomposition. If your pile is too large, the interior will not obtain the oxygen needed for adequate, odor-free decomposition. Most composting instructions suggest layering the material as the pile is built. This is not necessary if you are adding only leaves, I generally just add them as they are raked. If grass clippings are added, you might want to mix them with the leaves to prevent compacting of the clippings.
Moisture is an important aspects of composting.
Unless leaves are collected in a very wet condition, add water while placing them in the pile. Without moisture, the microorganisms will not function. Moisten the leaves to the point where it is possible to squeeze droplets of water from a hand-held mass of leaves. It is not necessary to add limestone to a leaf compost pile because they seldom become too acidic. Soil need not be added to the leaves either because there are enough microorganisms on the leaves to enhance decomposition.