Slicing larger steaks—from super-tender rib-eye to usually tough flank steak—creates multiple and flexible portions.
Slicing steak is a way of stretching more expensive cuts like rib-eye to feed more people (by serving slices you don't necessarily need to buy individual steaks for each individual at the table!). It's also a technique that renders more economical cuts like flank steaks fork-tender by cutting through the long fibers that make them tough in the first place.
Let the Meat Rest Before Cutting It
First things first: don't cut the meat right after cooking it. Let it rest. Smaller cuts need just 10 minutes, larger cuts can benefit from being left to sit off the heat for up to 30 minutes. Cover them loosely with foil and set them in a warm spot to keep the steak nice and warm while it rests.
Why let the cooked meat sit around before cutting it? Resting lets the juices in the meat, which have been sent scrambling by the heat, settle down and redistribute evenly through the beef, a process that creates a more evenly cooked and juicier steak.
Seriously, don't skimp on the resting time—you'll pay for it with a less evenly cooked steak that spills its juices the second you cut it.
Use the Sharpest Knife You Can Find
A sharp knife will help cut cleanly through the meat and avoid that ragged and slightly torn effect that duller knives can produce. It will also save you the time and effort of having to hack away or saw at the steak.
The knife should cut through the steak pretty much like butter. If you have to make too much of an effort, get your knife or knives sharpened!
Slice Across the Grain
Whether you're slicing filet mignon or skirt steak, cutting the meat across the grain will yield the most tender slices. Do this by cutting perpendicular to the long parallel muscle fibers in the meat, that way the fibers in each piece – which is where the bulk of any toughness comes in – are as short and thus as tender as possible.