Photographs, Own Experience, Observation, Imagination and Quest for order.
One of the best ways of finding inspiration as an artist is looking at other artists' work and learning from them. And the more you paint, the more you learn, and the more you are able to look at other artists' work and decipher what they were doing and their thought processes behind what they were doing.
Some places or content that most often inspire artists include a person, ocean, mountains, city. An artist could be inspired by a person through his experiences or his actions. An artist could be inspired by the calmness of the ocean or the serenity of the mountains.