Stay Positive
One tip I always give people when I'm coaching them on how to write more persuasively is to STAY POSITIVE.
We tend to "go negative" so quickly; we don't even realize we're doing it. But you have to think about the reader. The reader does NOT want to think about something really negative and sad and being stuck. They want to feel like PART OF THE SOLUTION.
So you want to frame it like..."we've made great strides in this area, but there's still a lot of improvement to be made, and with your help, we can do it..."
This allows you to pull the reader into the solution, not the problem.