For the best outcome, placing the steak in the freezer for 30-45 minutes prior to slicing it is essential. You should plan to slice it right after you remove it from the freezer. Doing so makes it much easier to thinly slice it as the steak stays in place. Using a very sharp knife is also immensely helpful. Last but not least, make sure to cut the steak against the grain. The muscle fibers are shorter this way resulting in more tenderness.