For most direct cooking, you want a medium-hot fire, though chops and burgers can benefit from higher heat. Fish and vegetables require a more gentle, medium heat. From this point, they'll take 20 to 25 minutes to reach medium-hot. Look for a layer of white ash over glowing red coals . No matter what you're cooking, wait until the flames die before starting.
Active flames mean the charcoal is still igniting and giving off a fair amount of smoke.
At this stage, not only will the flames char the outside of the food without cooking the inside, but the smoke is filled with unburned particles of fuel that will make your food taste somewhat like smoky ashes. Use your eyes and hands to judge the readiness of the fire. Also, since the rate of cooking is largely determined by how far the food is from the coals, you need the grate in place to determine the cooking temperature. For a fire that's less hot, wait 8 to 10 minutes and test again. When the coals have cooled to medium, the glowing red bits will be less apparent, and many of the coals will have turned yellow-brown.