Longer vertical lines will make you look thinner and taller. You can pick a fabric with the right pattern, such as vertical stripes. If you prefer monochrome clothes, then there are other ways of creating vertical lines. A V-cut neckline is one of them. A long scarf, necklace or a chain hanging down your neck will also create a vertical line. Horizontal lines are not bad either. A Breton shirt is a perfect example.