Good trimmed spare ribs won't have anything hanging off. Make sure you cut away any loose piece of meat or fat. This will dry out while cooking.
The last point is considered the most important trimming task for a good rack of smoked ribs, removing the membrane. The membrane is a layer of skin on the bone side of the rack. This tough material blocks flavor and smoke from reaching the meat and will make the ribs tough. Cooked at low temperatures the membrane will remain tough and will detract from the eating (the most important step). Removing the membrane can be easy if you do it right. Start at one end of the rack and with a blunt knife work your way under the membrane along the surface of the last bone. Using a paper towel grab hold of the membrane and peel it off. Some times you can get it in one grab and sometimes the rack is just stubborn and it might take a few tries to get the majority of the membrane off.
