Timeless design is the most “green,” environmentally sensitive thing I can do. When a room is created with timelessness in mind, it will still look as fresh, and function as well, twenty years from now. If you can’t tell when a room was designed, then you know it was designed well.
While you want to avoid trends at all costs, that doesn’t mean you can’t be creative. I like to use classic materials in a different way. For example, instead of using a square Carrera marble tile, as is traditional, I’d cut it in half to transform it into a subway tile, and maybe place it on a vertical rather than a horizontal grid. It’s the same classic material, but the look is updated.