Most of the time, I grill over high heat. I like things to move fast, I like the sound and smell of a very hot fire, and I gravitate toward dishes that you can get on and off the grill as quickly as possible. After a while, you'll know without thinking about it how hot the fire is: high, medium-high, etc. But until then, you can use the time-tested method of holding your hand about four inches above the grate and seeing how long you can keep it there. I know it sounds a little dangerous, but you'll pull your hand back at just the right moment.
High: 2 counts
Medium-high: 4 counts
Medium: 6 counts
Medium-low: 8 counts
Low: 10 counts

The most challenging thing about grilling is knowing when to stop! Without x-ray vision, how do you know what's going on in the center of the meat? Here are a few rules that make it easier.

Rule 1: Don't start testing the meat the minute it hits the grill. Don't attempt to pick it up, move it around, or turn it over every 10 seconds. Let it be! You need to give it a chance to sear on the bottom so that it naturally pulls away from the grates and doesn't stick. If you try to move it before it is seared, it will stick.

Rule 2: Don't cut into your food to see if it's done. It doesn't really work since you can't see inside and it lets the juices come pouring out and the food dries on the grill.

Rule 3: The best way to test for doneness is by pressing on the meat or fish with your finger. If you do this every time you grill, you'll quickly learn how to tell what a perfectly cooked steak or fish fillet feels like.