Be brief and say what you want.
It'll come off much better if it's well-worded but simple and to-the-point. The more fluffy sentences you add to your email, blog post, internet comment or product copy, the less professional it starts to sound.
Be direct in your requests, include enough details (pick the right ones!), say thank you, and cut out everything else.
Therefore, be brief when you can, but always..be polite.