self-important, considers themselves better than others. . It is not a compliment. Use it carefully.

I agree with David. In British English at least, this is normally a negative expression, for someone arrogant, self centred, cocky, bumptious ... (a ruder version is to be "up yourself"). Though I'm sure there must be a positive side somewhere. I am reminded of a scene in the film Coming To America, where one brother says to another, "Mother always said you were greedy." To which the other brother replies, "She meant it as a compliment!"

It's not a positive expression. It is used to describe people who are arrogant. Usual usage is "he/she is full of himself (or herself)". There's no genuinely positive way to use it.