Compost needs a few things. Nature provides all of them: carbon and nitrogen, moisture, oxygen, warmth, and microorganisms. Compost also enjoys movement, like being stirred or tossed periodically.
Articles and books focus heavily on the C/N ratio, or carbon to nitrogen. Yes, ideally you start with 20 – 40 parts carbon to 1 part nitrogen, but while that ratio speeds up the process, composting takes place even in a stack of damp cardboard at 500:1. It just may take a few years. Mix in some coffee grounds, vegetable trimmings, or grass to that cardboard and speed things up.
To get close to the ideal, just mix up stuff from trees (bark, leaves, wood chips, sawdust, cardboard and paper, twigs, etc.) and stuff from plants (vegetables, grass, flowers, fruit remains and peels, stalks, vines, weeds) and mostly vegetarian animal poop (horses, rabbits, cows, sheep, chickens, turkeys, etc.; birds eat lots of rodents, small fish, insects, voles and moles, but process food differently so its okay for composting.) If you get close to 1/2 and 1/2, great.
Too much nitrogen is rare, but if it does happen you will smell ammonia. The cure is to add more carbon.
In fact, smell is a great tool for the composter. If it smells like rotten eggs or poop, the compost is too wet and packed down. It lacks air. It needs “fluff.” Go easy on the water for a while, and add straw or twigs, wood chips, bark, or cardboard.
The only real “compost don’t” is meat, or meat-eater poop. Bad bacteria is the main reason. Unwanted animals is the other. E coli and other nasties come with the gut stuff. It simply is not worth the risk. Period. Don’t do it.
Unless you are in a big hurry, composting what you have works just fine, because no matter what your ratios are, the end product has close to 10:1 carbon to nitrogen. That’s exactly what your garden wants! How can that be? The result of the compost is the result of biology and chemistry Even if you failed chemistry and biology with honors, the next lesson will make sense. I promise.