Place it inside a strong, well-ventilated container suitable for its size and strength (cardboard box, dog crate, recycling bin etc.)
Provide some bedding material such as a tightly woven towel, blanket, newspaper or tissues. Make sure there are no loose strings or loops for the animal to tangle up into.
Place a hot water bottle (pop bottle is good) wrapped in a towel inside the container. This is essential for warmth and comfort even when it's a warm day
Cover it securely and keep it in a warm, quiet area. Please keep your pets away from the animal. They are seen as predators.
Do not attempt to feed it as this can cause additional stress
Always move slowly and quietly around the animal, and if you must, speak in a low, calming voice
If the animal is dehydrated (the skin "tents" when pinched; the eyes are sunken; the gums are pale), never give food but provide some form of re-hydration. Water, or a re-hydration fluid, can be given in small amounts. If the animal can lap from a dish...great! If not, use a syringe or eye dropper and drip small amounts into the corner of their mouths, making sure they swallow without choking.