Classic fireplace mantel would add to the fervor of the fireplace as a whole. Hence as the first step consider to paint the fireplace and the mantel. Consider the idea of hanging a large mirror or some fine art piece just above the mantel. If you do not want to place an artwork then think about the idea of placing antique over there.
If you can place decorative items on every side of the mantel it would look gorgeous. In fact a mantel clock is also highly recommended. Your idea in terms of decorating the fireplace is concentration on the center of the fireplace. You can keep candles in different colors. You should take care that the mantel is free from clutter. Also make sure that the ends of the mantel are equally decorated. Positioning of the items should also be according to the height and the length of the items. You have to ensure this to add great look to the fireplace mantel.