The key is to focus on your achievable objectives and what you are doing to reach those objectives.

For example: "Within five years, I would like to become the very best accountant your company has on staff. I want to work toward becoming the expert that others rely upon. And in doing so, I feel I'll be fully prepared to take on any greater responsibilities which might be presented in the long term. For example, here is what I'm presently doing to prepare myself…"

Then go on to show by your examples what you are doing to reach your goals and objectives.