Grilling: Here's what I recommend. Get your grill good and hot. The ideal temperature is one that will cook the steak to the desired doneness in the shortest amount of time without burning the surface. Place the room temperature steaks on the grill and close the lid. Watch closely to avoid flare-ups and turn when the sides start to turn gray and the bottom side has good grill marks on it. Flip and close the lid again. Continue to watch for flare-ups. When the sides are gray all the way through and the second side has good grill marks check for doneness.
Doneness: One of the biggest problems people have about steaks is how to know when it's done. Some people will cook up a small piece of meat with the steaks and use it for testing purposes. The only problem with this is that the smaller pieces will cook faster. I use what I call the stiffness test. Take the raw steak and place it on a plate. With your spatula or fork press down on the steak and move the spatula back and forth. Get a good feel for how the steak moves between the top and bottom. A completely cooked (well done) steak will have almost none of this motion. A medium rare steak will have a little motion but will feel stiffer. This is a skill that you have to practice with. Remember that you can always put a steak back on the grill if it's too rare but you can't uncook a well done steak. Err on the side of under cooked and throw it back on the grill if you need to. If you pay good attention to the way a steak cooks you'll get better at telling when it's just perfect.
Cuts: Another factor is of course the cut of meat and the quality of that cut. Finding the steak you like best, that fits your pocket book takes knowledge and experience. Read up on the subject, try different cuts, and of course, talk to you butcher. You'll have few better friends in this world than a smart and trustworthy butcher.
Resting: Now for the most important part, don't serve it right away. Let the steak "rest" for about 5 to 10 minutes depending on the thickness. This allows the juices to move back into the meat. Resting should be done in a place that is about room temperature and with only a loose covering over it. If you doubt me, try cutting a steak in half right off the grill. Let a second steak rest for five minutes, and then cut into it. See which one is juicier.
And of course the "real" most important rule is to practice. The more steaks you grill the better you will get. Be observant though. Every time you grill you should pay attention to the weather, the food, the grill. This is how you learn to be a great griller.