New Pile Not Heating Up
1. Take a handful of the compost material and squeeze it in your hand. If it leaves a shiny residue on the palm of your hand then the pile is too wet. Turn the pile more frequently than normal to add in some air. In an extreme case add some dry leaves to the bottom and middle of the pile when you go to turn it. If more rain is expected build your pile into a mountain shape to allow water to run down rather than into the pile.
2. If the moisture level is fine it may need more nitrogen in the form of green material. As you turn the pile add layers of coffee grounds.
3. If the moisture level is fine and you built the pile with a 1:1 green to brown ratio by volume then the pile might be too small to retain heat. Add more greens and browns. A pile that is 3 feet high will probably provide enough volume to solve the problem.
Older Pile Cooling Down
This is a normal part of the process. Finished compost cools to the point where it is slightly warmer than the ambient air temperature.
Heat producing bacteria are working as intended. Give the pile a turn to cool it a bit.
Compost Smells Bad or Weird
Like ammonia? Someone may have added manure or too much water. As you turn the pile add a scant layer of dry leaves.
Like sulfur? If you see large chunks of fruit break them up with a shovel. If the material is slimy add some dry leaves.
Does it smell kind of weird and some of the surfaces have a powdery coating? This is a normal part of the process.
The pile is too dry. When you go to turn it spray some water into the middle and top of the pile. If there is a forecast for rain shape the pile into a bowl so that it will catch and retain water. This problem can be avoided with frequent turning.
Insects (other than ants)
Creepy crawlies do the important job of shredding material and are a normal part of the process. When the compost is complete they will wander away.
Always complete a new pile with a layer of browns. Turn the pile frequently to scare mammals away.
Weeds Growing in the Compost Bin
After turning the pile dig up any weeds you see and toss them into the green receiving bin. Keep the perimeter of the bins well mulched.