Tips for an Effective Message
Be Careful
It's very important that you carefully review and edit your message before you 'Send' it because after you press the 'Send' button at the bottom of the form, the message is on it's way and there is no way to get it back. You might want to consider drafting the message in a word processor or text editor and then copy and paste it into the mail form.
Be Nice
To ensure that your message is well received it's important that it be written in an even-tempered tone. Being passionate about an issue and taking the debate about an issue personally by slinging expletive laced insults are two different things, with the latter not being constructive in the slightest. If you're unsure about the tone of the message you've written try leaving it for a few hours and then reading it again later, or have someone else read it and give you feedback.
Be Specific
The best feedback is specific feedback. If there is a specific proposed plan or action you don't like, mention which one it is and why you don't agree with it. Details and facts weigh heavily.
Offer Alternatives
Be part of the solution. Offering alternatives to specific issues you don't agree with is a great way to drive the process.