Telling stories is the best way to illustrate your work. If pictures can be incorporated to show the people in the story, that's even better. And of course the stories are picked to describe how one person benefited from what you do. How clients benefit is easy. How donors benefit requires a more subtle and thoughtful explanation, and would be fantastic if actually quoted by a donor.
A few charts are good - they make incomprehensible numbers more understandable. And if you have lots of numbers you feel must be made public, how about a reference to their availability by contacting the office and you'll send your audit or financial statement.
The best way to check your writing is to ask yourself a very basic question. "What do I want people to know, think or feel after they read this?" If you start with that you'll probably have an easy time figuring out what to say.
For more nonprofit administration and management tips, as well as nonprofit funding and endowment development, subscribe to Endowment Development Institute's Newsletter here.