Know the signs
Signs an animal may be neglected: no food or clean water, no shade or shelter in heat or storms, a coat matted with filth, open wounds or a limp that is not treated, ribs and hips showing, or a dog chained with no relief. Do not argue with the owner or go onto their property. Write down what you saw, where and when.
Noticing carefully and telling the right person is how most animals get help.