Okay, here we gooooo ...

1. To prepare, get some comfortable clothes. Seriously, that's about it.
2. Find a meditation teacher. Many Buddhist temples will teach meditation for relaxation without any religious teachings, you can also find teachers at places like the YMCA and others.
A) A teacher is important because they can guide you though the meditations, watch how you are reacting and help answer your questions. Websites, book and CD's aren't very interactive.
3. Have an open mind. That's all you'll need. Oh, and comfortable clothes again.

4. I separate this one because it's more advice than anything. Don't worry about what you "see" when you first start meditation. It's different than anything you've done before and can be a little weird at first.

If you have any specific questions, feel free to ask. I've taught meditations for relaxation at the local college and spent a considerable amount of time in more advanced meditation myself and can hopefully offer something of value if you need.