Always let your steaks come to room temperature (70 degree F.) before cooking or grilling. If your room's temperature differs from 70 degrees F., then just adjust your time accordingly.
A cold steak will contract when it hits the heat and this wall cause it to toughen. This is possibly the first biggest mistake people make.
Remove your steaks from the refrigerator at least 30 minutes before you plant to cook them - sometimes as long as 60 minutes (depending on size).
Pat the steaks dry with a paper towel. You want to have a completely dry steak before cooking. If you steak is wet, you will essentially be steaming it
Do not salt your steaks just before cooking. I know that some people do salt their steaks before cooking, but trust me and don't salt - the result will be juicy, delicious steaks to serve your family and guests! Salt after the steak is cooked to your liking, has rested the required time, and just before serving.
Salt brings moisture (water) to the surface of the steak, and the water sits on the surface as you cook the steak. Thus, you are again basically steaming the steak. Traditionally, when browning meat, chefs skip the addition of salt because the salt draws water out of the meat's surface through osmosis. If, for example, you were to season a steak just 10 minutes before grilling, beads of moisture would appear on the surface, eventually forming a shallow puddle of juices. On the grill, the steak would turn gray, not brown.