This is what I do and seems to work good for me (22" WSM & RO Lump & Foiled clay pot). I fill the coal bin, and leave an indent on the oppisite side from the lower vent I plan to leave open and work with. Usaully the one oppisite the wind direction. Wind seems to be my biggest enemy.
Once the heat gets to within 30* to 40* from my target temp, I will close 2 of the bottom vents completely and start watching the rate of increase, slowly closing the remaining vent until it slowly reachs my target temp and let it sit there for 15 - 20 minutes making sure the white smoke is all gone.
Then I add the meat and unless the wind becomes a factor, it will maintain that temp.
22.5 WSM, 1997 Performer, 1984 Kettle, GMG Daniel Boone, Mini WSM