'Cat fan, work your way UP to the temperature you desire. Start your fire with plenty of lump (don't be afraid to take it up to within an inch or two of the top of the firering) and then close your dome, open your vents and let the temperature climb and stay close by. When you get about 50 degrees (say around 190) from your desired temperature (using 240), start closing the vents down. Close your daisy wheel on top so that only about half the holes in the daisy are showing. Close the bottom to about 1/2". Then when the temperature gets within 20 degrees (220), close the bottom even a bit more. When the temperature gets where you want it (240) close the bottom vent down to about 1/8-1/4". If the temperature should drop , open it up an 1/8". It may still drop for a few minutes before starting to rise. Have faith. Don't be tempted to open it too much.
At some point during this process (say when you hit 200 or so) you can put the meat on (and your wood chips if you desire). When you do, put it on quickly and close the dome back. If you leave the dome open too long the fire will start to take off a bit on you. Leave the settings exactly the way it was before you put the meat on. Allow the temperature to stabilize again and continue to tweak it until your temperature is stabile at the temperature you want. Once you adjust the vents give it 10 minutes to see what it is doing. After opening and closing the dome, give it ten minutes.
Then, once you have your temperature, leave it alone. Check it after 30 minutes and tweak again if necessary. Check in another 30 minutes. Once you have the same temperature for an hour, you know you are set. Leave it alone. Come back in about 8-10 hours and check the temperature of the meat and decide how it is coming along. If you're running out of time, you can always boost the temp at the end for an hour or so. Don't take it above 350 or you will wind up with too much burned meat.
I have learned that keeping it at 240 is not that difficult. Keeping it at 220 is harder. And oh yes, check your thermometer. One time I was having trouble keeping my temperature down to 240. After I completed my cook and the Egg had cooled, I noticed I was still registering 120. My thermometer was off by 35 degrees and I was cooking at a dome temeprature of 205. It held it nicely once stabilized but that was way too low.