Don't take it off of the grill until it is done! LOL.
The big thing to be aware of is the stall. Sometime between 145-170, usually around the 160-165 mark you might see the temp stop increasing for long enough to cause concern. You won't be able to ignore that concern and it will really mess with your head, just remember not to act on it. Let the grill do its thing. You can wrap in foil at that point and a lot of us do. That will push you through the stall faster but does have some affect on your bark. I wrap when the stall hits if I am on a set time frame, otherwise I let it roll. You might even see the internal temp drop a degree or two during the stall. This is normal and is just a cooling process from the fat rendering and causing a cooling effect similar to the human body sweating. The stall lasts 20-30 minutes sometimes, and sometimes (especially with brisket) can last 1-2 hours. It still messes with my head but now I actually enjoying waiting it out to see how long it will last. Each piece of meat is different.
If I don't wrap, I leave the lid on until I hit around 198 unless my cook is going long and feel the need to check on the amount of coals left in the snake. At 198, I will use a probe to see if it slides in and around like a hot knife in butter. If that happens, its done, if not I let it go another degree or two then repeat.
I like to use a pan of water on the coal grate. Helps keep some moisture as well as acts as a heat sink that prevents big temp swings. I've recently switch over to putting a pan of baked beans in place of a water pan.....drip beans are the bomb!
The snake method works great. If you haven't done it before, just remember its easier to opening the bottom vent to raise temps than it is to close it down and lower temps. The good news is that pork butts come out really good anywhere from a cooking temp of 225-325, so if you are running hotter than the typical slow n low 225-250 don't' worry about it. I usually run my top vent wide open and the bottom slightly cracked with a 2x2 snake on my 22's. Since I've had my slow-n-sear which requires the top closed about halfway I've seen that shutting down the top a little bit does help extend the length of your coals. If and when you adjust your vents, let it sit for at least 15 minutes to let the new adjustment settle in. Also, if you are using wood chips instead of chunks, make sure the piles of them on your snake are separated. If you piles run together the chip will burn from one pile to another quicker than intended lighting your coals quicker than intended along the way.
Update: Everything above my post is absolutely correct as well!