Letting your beef rest after cooking is as important as the cooking itself. This goes for all meats and all cuts. Once you pull the meat out of the pan or oven or off of the grill, put it on a cutting board and let it chill for about 8-10 minutes, longer for larger pieces of meat.
If you cut into meat right after cooking, all of the juices will run out, leaving the meat dry and tough. While meat rests, it re-absorbs these juices and the amount of ‘doneness’ becomes consistent throughout piece of meat. This is probably the most important rule when cooking all meats.