A very talented marketer friend of mine reminded me the other day that it's not always what you say that counts, it's often the way that you say it.

One thing that can ruin your credibility faster than a very fast thing when it comes to your marketing communications is bad spelling! Don't rely on spell checkers and don't check your own work. You'll tend to read what you think you've written, not necessarily what's on the page.  Get someone else to read through your work BEFORE you press the button.