The key, really, is to be patient and start your fire plenty early. By starting the fire at least an hour before you want to start cooking, you can light your lump coals in the center of the coal basket, set the upper and lower vents to where you know 250 degrees (Low and Slow cooks for example) can be achieved, and then let nature take its coarse. For me, 1 hour will achieve the 250 degree temp and allow it to sit at this temp for a while. You know you are good when the fire temp stabilizes at desired temp and stays there for a while before you add the meat.
If you want to speed the process up yet still maintain the lower temps....you gotta stick around and watch the temps... I have opened the vents wide open before on the the low 250 temp cooks, but as the Temp gets close to 190 or 200, i start backing down the openings of the vents (to where I know 250 will be maintained)....if you keep everything wide open UNTIL you reach 250, then you are going to overshoot the desired 250 temp. Now you will have a bit of troube maintaining the lower 250 temp.
As for overshooting the temp and trying to lower back to 250...I suppose you could cut off air flow completely and watch the temps go down...and when close to 250 on the guage open the vents back to the desired position for 250 cooks...?? This seems complicated and harder to achieve. I think patience is the key....dont open vents too much at the start. Plan for extra time to get to 250 slowly...then you are golden!
"In the midst of a busy life, take some time to be a kid again." -- Fortune Cookie
Her name is Kahlan !