1) Choose the right cut: Start with a great product. Whether you like filet or strip or ribeye, I tell people to get 1.5 to 2 inches thick so you can get the char and temperature right. If you go too thin, you can't get the char.
2) Cook at a high temperature: A really high temperature will sear the meat and seal the juices, the flavor, in. A gas grill won't get hot enough, so keep the lid closed for 25 to 30 minutes to bring the temperature up.
3) Don't bother marinating a premium cut: If you have too much oil on a steak, you start a carbon fire, which isn't the char that you're looking for.
4) Buy more than you need: When I'm cooking for four people, I get five steaks. On the fifth steak, I'm slicing and checking the temperature. Anyone standing nearby will be more than happy to taste the test cuts.
5) Slow down: Resting meats is very important. Let it sit three, four, or five minutes before you cut into the steak, otherwise you loose the flavor that you sealed in by searing.