Well, first of all, self-care is easier said than done. Second, self-care is a shift of priorities. Instead of placing others' need before your own, you place your own need before others'. For example:

You are exhausted and need to catch up on your rest. But someone wants you to take her to the airport. Will you prioritize your need for rest by telling her that you can't?

Again, easier said than done. Hopefully, it gets easier over time though.