So, instead
of just using an adjective to describe yourself, mention previous experience and responsibilities, as well as your
accomplishments (for
example, any goals or targets you hit).
The best way
of proving that you offer what the company needs is to come up with a list
of your daily responsibilities, the major projects you've worked on, projects you've worked on that you weren't asked to do, recommendations or endorsements from others inside or outside the company, future responsibilities,
examples of how you've made your boss's job easier, and, if possible, quantify your
accomplishments, don't mention that you work hard (
so does everyone else) or that you've been with the company for a long time.