Install the fan adapter into one of the holes of one of the lower vents. There should be aluminum foil tape to cover the other holes in that same lower vent. Close all the other lower vents all the way. You want one hole with the fan in it as your only possible source of air for the fire. The dome vent will be 100% open all the time when using a GURU fan.
There is a slider door damper on the fan housing. When you need to choke back the fire that is the one you will use and it should close off the only source of air to the fire. Also sometimes in windy conditions you need to partially close it as the wind can blow through the fan intake.
Usually I close my fan damper about 80% of the way when I first start the
WSM to choke back the freshly lit coals. My typical start is full chimney of lit dumped over about 1/2 to 2/3 ring of unlit (basic classical minion method), close the fan damper about 80% to get those fresh lit coals under control. Then once the pit stabilizes at 225 for about 10 or 15 minutes, on goes the food and open the fan damper to 50% or more depending on weather conditions (wind, temp). I usually run it at 50% for the first part of a smoke as I have a 10cfm fan on my 18.5"
WSM so it's a little overkill. Basically as long as the fan is not running most of the time, leave it as is. When the fan starts running more, I open it up. If you use less lit to start your
WSM you may not need to close the fan damper at all. Just watch the temps on the Guru and if it starts running higher than you want, then choke it back by closing the damper. And yes, I have closed it all the way before on a really hot fire and a hot day. When you make a damper change give it at least 5 minutes to settle down and fire temp changes are not instanteneous. 10 minutes may even be better, then look at where your temps are. If they are swinging down and close to or below your desired temp, then open the damper slightly and wait again. If you fiddle with the damper too often you will be chasing the temp like using regular dampers. Let the fan and computer do the work for you and use the damper to cool down a hot fire only.
Top vent is open all the way and never needs to be touched. Short of a grease fire in a
WSM I have never seen any need to touch the top vents - 100% open 100% of the time.
You will see the WSM will run rock solid for hours at the set temp with you not needing to fiddle with any vents or anything. A Guru is a great addition to a WSM and you will soon be wondering how you ever lived without one. Since I got mine, I get a full nights sleep on overnight shoulder smokes. Basically as long as you have fuel, it will hold temps. Think of the Guru as your little helper minding the pit while you sleep.
I do know the 22.5" model burns through fuel faster than the 18.5" model I have, but after one or two smokes you will know the pattern and at what point you need to reload fuel on a long smoke. The greater fuel burn is due to larger pit size and more food mass if fully loaded.