How bad is the rust? It is just some surface rust or is it actually rusted through? If it's just some surface rust I would take a grinder, steel wool or a wire brush and get it off of the smoker. It all depends on how bad the rust is. One the rust is gone then spray the inside of the smoker and racks with Pam or Olive Oil and fire up the smoker and apply smoke to the rig. If it was your first time using it I would usually slowly bring up the temps to make sure to burn out all of the oils that may be in there and to also make sure you don't burn off any paint or anything but if the smoker has been used before I would normally just spray it and then run it for a few hours then throw your meat on. People probably have more in-depth processes so lets see what they say.