Well, my biggest mistakes were, when I moved away from my little Weber kettle to a New Braunfels Smoker was...
#1. Not giving enough time.
#2. Not being familiar enough with the equipment to do a good job of fire control. (Too hot).
#3. Being afraid of ruining a cut of meat by trying something new.
#4. NOT using a water pan in my old Silver Smoker. (Beer cans in the smoke chamber opening work quite well.
#5. Opening the door WAY too much...
On the care and feeding of a smoker perspective my mistakes were...
#1. Not cleaning the firebox of ashes after it cooled down.
#2. Storing the smoker directly in the path of the rain.
(Water and ashes make a considerably corrosive mix).
#3. Not repainting the pit every season. These things loose paint awfully fast, and need to be touched up. I now buy my Krylon BBQ paint by the box.
New Braunfels Bandera Smoker. Silicone Door Gasket mod. HD Alum Foil baffle. In door thermometer. 3 hanging thermometers.
Weber Smokey Joe Gold portable BBQ Grill for those beach weekends!
152qt Igloo ice chest full of Jello shots and beer.