Imagine: you are in Ancient Olimpia archaeological site. You walk on the grass. Here and there you see traces of an ancient civilization. You try to imagine the life in that piece of word. You breathe to find other clues. Is not easy. Then, you turn the corner and you find an ancient wall. On the wall a painting that recalls in your mind all the imagine you search in your fantasy.
This is the approach i used when i worked on my illustrations.