You Must Care About Your Work
In order to do anything with excellence, you must truly care about the finished product. That "product" may be a sales transaction, a feature film, or a policy and procedure manual; whatever it is there needs to be a level of ownership and responsibility.
Ideally, you are able to get paid for the thing you're good at and that you care about. That's the dream job, and you will be self-motivated for excellence. But that's not always the case.
Other times you may have a job you're not passionate about. It's hard to care. But that doesn't mean you can't take ownership and care enough to do it well. Whether running a company or delivering pizza, choose to be excellent, and care about that.