The separation of "self" from the rest of Existence is an artificial distinction. However, such distinctions are sometimes quite useful for improving mental properties such as self-awareness or ethics.
Typically, a common "individual" soul is attributed to everything that lives in a single human brain. Here are some other possible ways of distinction:
Since there is no boundary between you and the world, it is unwise to treat the world in a way you do not want to be treated.
If you believe in individualism and competition, you should also allow the various parts of your ego and body to be individual and competitive against each other.