It sounds so corny and clichéd to say this, but if you want to feel beautiful, you have to define beauty on your own terms. It's one thing to look to celebrities for trends, but it's another to think that looking like Heidi Klum is the only way to be pretty. (After all, even Heidi admits she has those off days.) The more confident I am, the less I worry about a huge pimple or whatever; the more I remind myself to be accepting of myself, the more I appreciate what my body does for me.
To help women and girls develop better body images, the NOW Foundation holds an annual poster contest. The goal is, as the contest puts it, to show that "beauty is not limited by body size, body type, ethnicity, age, or physical appearance." So if you're artistically inclined — or if you have a little sister who is — consider entering. (You have until the end of December.) Otherwise, check out this collection of past winners when you're getting self-critical.