Being a Tumblr girl is about creativity and dedication to your style—it doesn't have to be expensive. If you have long hair, style it in different ways. And honestly there is no exact way to be a "tumblr girl" so don't sweat it. You will only build a following if people think you have something new and special to offer in the way of style inspiration. Do something new every few months, either changing the color, letting it grow out, cutting it short, or buzzing it on the side.