Setting Boundaries

I've been told I need to learn how to set better boundaries to protect myself. That's hard to do when by nature I'm a very open and accessible person. I do, however, understand the necessity of making sure that people can not walk all over me. How do I do that and still remain true to my character? How do I set boundaries without hurting people or shutting them out? How do I learn to speak what I'm really feeling? I feel a bit daunted by this task but determined to learn. As I crawl under the quilt tonight, I will ask my God to give me the wisdom I need to set boundaries, to help me remain soft and accessible, the way He made me, and to continue to learn and grow as His child.