Because of the danger of disease transmission, human and pet feces should not be composted. Meat scraps, bones, and fats will likely attract rodents and other unwanted visitors. Less experienced composters should avoid materials heavily infested with weed seeds, insects, and disease organisms. Although a properly managed compost pile should generate enough heat in the center to kill most of these pests, ensuring uniform heat may be difficult, particularly in a small compost pile. Although commercially packaged compost starter is available, adding a little soil or finished compost will supply all the microbes you need for composting.
Microorganisms require a proper environment to work efficiently.
Any factor which affects the microbial population will also affect the rate of decomposition. Nitrogen is needed by the microbes in order to break down and use the carbon found in organic materials. The ratio of carbon to nitrogen in the compost pile will affect the rate of decomposition. If the carbon content is too high, decomposition will be slow. If the nitrogen content is too high, ammonia gas can be given off, creating foul odors.