Your pony tail palm, Beaucarnia, is often grown as a houseplant where it grows best in bright, indirect light and can get by on very light watering. Outdoors it is hardy to about 25 degrees F. and thrives in full sun with moderate water once established. It looks like it is in a pot within a pot. If so, when you water take it out of the cover pot, and water in the sink and allow it to drain out completely before returning to the cover pot. If the plant sits in water, it may lead to root rot. Also, Beaucarnia are sensitive to salts in the tap water. If the brown tips continue, consider switching to steam iron water available at your grocery store. Do not over water. Water only when the soil feels dry down to the first knuckle.