Wonder why your tomato slices aren't perfect like the ones on your favorite deli sandwich? It's probably not your technique; it's more likely that your kitchen knife is dull. A dull blade is going to make you work harder as you slice. You'll also use a heavier hand to pierce the tomato skin, and that heavy hand does two things: It increases your risk of cutting yourself, and it increases the mushiness of your tomato slices.
Aside from the obvious tip of sharpening your blade to make slicing easier, try using a serrated knife, such as a bread knife. You may have better luck keeping your slices firm and intact because the serrated edge won't have any trouble piercing the tomato's skin. Slicing tomatoes is also a great task for your kitchen mandolin, egg slicer or meat slicer for perfect, uniform slices every time.