ring of coals around the top and bottom and it works out practically perfect. I'm lazy and like the simplest way to do something. :-)
Maintaining Even Heat
No matter how evenly you distribute your coals above and below your dutch oven, there will be some spots that get hotter than others due to wind, quality of fuel, and phase of the moon. To prevent burned and raw portions of your meal, you should just rotate your oven occasionally, maybe every 10 minutes. You can do it however you like, but I've got an easy way - remember, I'm lazy.
Lift the whole oven off the campfire cookin coals by the wire bail.
Turn the oven clockwise 1/3 of a revolution.
Set the oven back down on the coals - with three legs on your oven, it should sit in the exact same spot it started in with coals between the legs.
With a lid lifter or pliers, grasp the lid handle.
Twist the lid counter-clockwise 1/3 turn - the logo on the lid should be in the same position it started at.
I like this way because both the top and bottom heat moves in relation to the food inside and there's nothing for me to remember except that the lid logo always looks the same.
Taking a quick look inside at this time will give you an idea if the coals are cooking too fast or slow. Just be careful to not drop ash in or let heat out.
Maintaining Long Heat
Your first batch of coals will probably keep the oven hot for 30 to 45 minutes. That's long enough to cook most things, but you sure don't want to let the oven go out for those 1 hour or longer meals.
Just make sure you check your oven every 20 or 30 minutes to see that the coals are ok. Where you see spaces with just white ash, fill in with a few more coals. Or, you can just brush all the ash and coals away and put on a new batch all at once. If we're just sitting around the campfire cooking s'mores, talking, or playing cribbage, I tend to do the former but if the fish are biting I do the latter so I don't need to keep checking on it.
Stacking Heat
When you really get going and have 3 or 4 dutch ovens outdoors cooking, there is a lot of ground space chewed up and a large part of the heat from the coals is heating the surrounding countryside instead of the ovens. I recommend that the first dutch oven you buy is a 12 inch model and then your second purchase is a 10 inch model. This allows you to stack the ovens.
Stacking your dutch ovens is a great way to save ground space, fuel, and time - besides, it looks really cool to have 3 ovens making a tower.
The coals on the lid of one oven serve as the 'underneath' coals for the oven stacked on top. And, the oven on top helps trap heat for the oven underneath. All this makes heat estimating more difficult so you should only tackle this after you've got some experience and are willing to practice on a few meals.
The most important thing to remember is that items needing more heat should be on top. Your bread or dessert should be the bottom-most oven since it wants very little heat underneath. Then, your meat to roast in the middle and a stew on the top. It takes some planning, but an entire meal can be fixed this way so it all gets done at the same time.
Rotating stacked dutch ovens takes a bit more work. Take off the top ones, rotate the bottom one, and then work your way back up the stack. Move as fast as you can without spilling so you keep the ovens hot.
Temperature Tips
Finally, just a few tips to tuck away for later:
You can cook food, but you can't unburn food. Use less heat and cook longer rather than overheating.
Preheat your dutch oven for frying or searing meat. Otherwise, put the food in cold and let it all heat up together.
Keep adding wood to your campfire to ensure you have a supply of camp cooking coals available. If your fire burns too low, it may take extra time to finish your cooking while you make coals.
Some briquette users just set new briquettes next to burning ones around the dutch oven so they light and