Actually, it depends. It's based on one of the big rules about "the." Use "the" when there is only one thing. For example, the sun, the moon, the Internet, the environment.
So, for jobs, here are some examples:
As the president of ABC company... (a company only has one president)
As the Vice-President of the U.S.... (the U.S has only one VP)
As a Vice-President of IBM,... (most companies have many VPs)
As the editor of the New York Times... (this means you are the top editor, editor-in-chief -- only one of you)
As an editor of the New York Times... (this means you are not the top editor, just one of many editors working on one part of the paper)
For Creative Director, it depends. In some companies there is only one creative director so you use "the." In other companies (like advertising agencies) there are many creative directors so you use "a."
Also! You can use "the" when you are describing something very specific and giving specific information so we know exactly which one you are talking about.
He's the reporter who broke the story about the budget scandal.
She's the vice president in charge of sales.
They're the salesmen I was telling you about.
I hope this helps!