C:N Ratio
This is proportion of carbon to nitrogen in your compost unit. The ratio will affect the speed of composition. Ideally, your C:N ratio should be 30:1. Grass clippings and plant trimmings and kitchen scraps are high in nitrogen. Sawdust, straw, wood chips and dry leaves are high in carbon. A mixture of kitchen and yard waste should give you close to the ideal ratio.
A pile that is too high in carbon will stay cool and sit a long time without breaking down. A pile too high in nitrogen will smell like ammonia gas. In both instances, the decomposition process is working on everything organic. If you have the time to wait and the space to keep these materials, you'll eventually be rewarded with compost.
Water and Air
The right amount of water and air to keep the biological and chemical processes functioning. A compost should have the water content of a wrung out sponge. The "squeeze" test is an easy way to gauge the moisture content of composting materials. The material should feel damp to the touch, with just a drop or two of liquid being released when the material is tightly squeezed in the hand.
Containers
A composter can be made of wood, concrete blocks, wire mesh or almost any material you have available.
The three most essential features in a composter are:
1. A lid that protects the pile from rain and snow and allows you to control how much moisture gets in.
2. Holes or vents to allow air circulation
3. A means of removing the final product.
Some design ideas:
~ a wire mesh bin with a hinged front panel
~ a three sided cement block bin with an open front that allows you to turn the pile and remove the finished compost.
~ a circular unit made of chicken wire or snow fencing that can be opened up to collect the finished compost.
~ a metal barrel or garbage can with holes punched in it and the bottom removed.
~ for more advanced enthusiasts, a unit with several compartments can be used to manage compost at different stages - raw materials, active piles, and finished product.
A compost pile should be large enough to hold heat and small enough to admit air to its center. As rule of thumb, the minimum dimensions of a pile should be 3 feet by 3 feet by 3 feet (1 cubic yard) to hold heat. The maximum to allow air to the center of the pile is 5 feet tall by 5 feet wide and as long as you wish.