1. Simple - Good stories are easy to understand. Simplicity also aides in memorability, because the overall lesson is easy to grasp in summary. Remember that you are not trying to impress, but to share an experience.
2. Emotional - Good storytelling requires an emotional component. Most of the memorable ones have humor, pain or joy (sometimes all three). If every story were simply facts, most of us wouldn't listen or remember any of it.
3. Truthful - You need to believe in what you're saying and be honest with yourself and your audience about it.
4. Real - Good stories are first-hand experiences that you actually witnessed. Even if it's a story that's passed on generationally, an effective one still has an element of how that story relates directly to you and told in your own words.
5. Valid - Regardless of the audience size, a good story works for any audience. One to one-million. It isn't concerned with how many people can hear it, just that someone, somewhere is listening to it.