"THE FIVE FREEDOMS" promoted by the Farm Animal Welfare Council (fawc.org.uk/freedoms.htm) to protect farm animals can be applied to shelter animals, too:
1. Freedom from Hunger and Thirst — by ready access to fresh water and a diet to maintain full health and vigor.
2. Freedom from Discomfort — by providing an appropriate environment including shelter and a comfortable resting area.
3. Freedom from Pain, Injury or Disease — by prevention or rapid diagnosis and treatment.
4. Freedom to Express Normal Behavior — by providing sufficient space, proper facilities and company of the animal's own kind.
5. Freedom from Fear and Distress — by ensuring conditions and treatment which avoid mental suffering.
For more details on The Five Freedoms for shelter animals, please read the column by Lila Miller, DVM in Animal Sheltering magazine (pdf), published by the Humane Society of the United States.
