When writing persuasive messages, it is important to give special attention to the analysis of your purpose because you want readers to understand what it is you are trying to communicate -- and why it is so critical for them to understand the point of your communication.
What are you ultimately trying to say? Why is it important for readers to grasp what it is you are saying? How can you get across the purpose of your message in the most impactful and memorable manner? These are questions to ask yourself (and to keep in mind) when you are focused on analyzing the purpose of your message.
For any messages that you write: Always review your text multiple times for punctuation and grammatical errors. Aim to avoid run-on sentences. Look for fat to trim: If you have text included that is not totally necessary to the message you want to convey, cut it. The more to-the-point you are with your message, the more impactful you will most likely end up being.