1. What is the point of what you're writing about? Find out the concerns your users have and then demonstrate why you are the best choice to solve that problem.
  2. If you're not much of a writer then record how you would say it with a face-to-face customer, and then type it up.
  3. Just get started. You're going to have bad ideas. The sooner you start writing the sooner you can get rid of them. The blank piece of paper is the worst part about writing content, just embrace it and put your initial bad ideas down on it.
  4. If you seriously can't do it, then don't. You wouldn't drive a bus if you didn't know how. You shouldn't write content if you can't. Give it to someone who can. Your colleague, a professional copywriter - whoever really. Just give it to someone who can do a great job at it.
  5. Share often. You're not a magician, saying "ta-dah!" when you're done isn't going to leave your audience gasping at the sheer brilliance of what you've produced. No. Every time you do something, share it with someone. Say, "Hey, do you think this is clear enough?" Speak to your web agency - they probably wont be copywriters but they read and work with enough text to know what will work. You're paying them for their consultation, use it!