I've smoked many turkeys and developed a pretty consistent method that seems to please most folks. The one problem with smoked turkey is that the skin is not the right crispy brown texture that folks are used to out of the oven.  Properly smoked, it doesn't get hot enough to crisp the skin so the skin is just discarded.  So I always serve the turkey already carved and don't carve it at the table.  You can also skin the bird before smoking, but I leave it on as it is holds in the moisture a bit.

1) Brine overnight.   Fully submerged.  I use the ratio of 1.5 cups kosher salt + 1/2 cup brown sugar + 1 cup white sugar in 2.5 gallons of water.

2) Use injectable marinade of your choice.  It needs to have a lot of butter and/or oil in it. You can find recipes online or some of the pre-packaged injectables like Cajun Butter are good too.   Simmering garlic in melted butter or oil, then straining out the garlic and injecting the cooled oil is easy and tasty. There is no point to injecting water-based marinades after you have brined.  Some broth or apple juice is OK as they add flavor, but mostly you want some oil/butter in there.   Stay away from black pepper and paprika in the injection as they change the color of the meat and people think it looks weird.

3) Cover the bird with a layer of wet cheesecloth when you put it in to smoke.  This catches the blackness from the smoke soot but lets the flavor through. Makes for a better-looking smoked turkey and keeps the meat nice and light colored.  You want the black meteorite look on brisket or pork shoulder, but not turkey.  Also gives you an idea of temperature.  If it starts to stick to the bird, you're cooking too hot.  It should lay on top like a blanket. 

3) For the wood to cook with, my preference for turkey has been apple.  Close second is pecan.  Cherry tastes good, but the cherry I have really darkens the meat a lot.  The drumsticks look like ham inside with the darker smokes like cherry/hickory/oak.   Oh, and I never got compliments when I tried mesquite.  People didn't like it.  If you've never somked before, be aware that smoke leaves a pink-reddish color in the meat.  Even the lighter colored smokes like apple impart a bit of color.  People that aren't used to the color often think the pinkness is from not being done when it is actually smoke color in the meat.

Cook at 250-275. If appearance isn't all that important to you, I prefer to take the wings and leg quarters off and smoke the parts separately.  Keep an eye on the thighs/wings/drumsticks as they will be done before the breast.   Get a good instant-read meat thermometer and trust it.  If smoking the bird whole, wrap off the drumsticks and wings with foil when you have 160 degrees in the thickest part of the leg.  They will continue heating but more slowly with the foil on.  Then continue cooking until you have 160 in the thickest part of the breast.  Yes, I said 160.   Take the bird off and wrap it tight in foil to rest a while before carving. It will be 165-170 after it rests.  The dark meat will be hotter, and you want the thighs to be 170-180 to make sure the bone doesn't bleed when you carve. I rest it upside-down from the orientation I cooked it.   I normally cook breast down and rest breast up.  At 185 degrees, it falls off the bone and doesn't carve into nice slices.  Makes good meat for sandwiches though.  (I overcook turkeys and pull the meat like pulled pork and freeze it to save for lunch sandwiches sometimes.  Sure tastes good in the tractor!) 

If your bird has one of those silly pop-up timer things, ignore it.  Or better yet, remove it before you start.  I ruined many turkeys when I relied on those things. Sometimes they pop at 170.  Sometimes 200.  Sometimes you can melt them and they never pop.  Almost everyone overcooks turkey.  The old rule of thumb about 180 degrees is to get the stuffing done so you don't give your guests food poisoning, since that is traditionally the way turkey was prepared.  Turkey properly handled and cooked to 160 without stuffing is safe and much moister. 

Cooking time in a smoker varies wildly with weather, fuel, bird size, how cold the bird is when you put it in, etc.  I really prefer to cook my turkeys the day before, but have done it on the same day before and gotten up in the wee hours to get started for a noon-ish meal.   If it were me, I'd plan 7 hours for a 12 pounder, but that's on my pit.  Don't know yours.   I'd expect 5 hours to cook it.  1 hour to rest.  1 hour to carve and platter.

If you are smoking the day before, just leave the turkey in the foil it is resting in. Leave it rest for at least 2 hours before chilling in fridge until you need it.  Just leave it in the foil and rewarm it in the foil in the oven or roaster or even big crock pot at 200 degrees until hot through.  Then carve.

4) Carving the whole bird hot makes better meat than chilling/rewarming the cut meat.  Remember the oil/butter in the marinade?  It's still in the meat.  As soon as you cut the bird, you start to lose it.   Best to lose it on the platter than in the fridge.  Carve in a lipped tray or a foil pan to catch that liquid that comes out of the meat.  Pour it back over the cuts on the platter.  Best tip I ever got for carving hot meat was from a fellow competitor at a Steak Cookoff Association contest:  Wear a pair of string knit utility gloves under a pair of nitrile doctor gloves.   Makes the heat bearable so the sweat in your gloves doesn't scald you. 

For the giblets and neck, I have never attempted to do anything with them on the smoker.  I simmer them in a pot in the house for a couple hours. Makes the house smell good. I pull the meat off the neck and finely dice the giblets (think giblet sawdust) and stir into gravy.  I like a thicker gravy than most.  Properly smoked turkey doesn't need the thin gravy to be edible like baked turkey does..... The gravy is for the mashed potatoes!  You can stir some of the broth/stock from simmering the giblets into the potatoes and dribble on top of the cut meat to keep it moist too.