I've been thinking about geting mine ready tommorow, its supposed to be Highs in the upper 30's and low 40's here in Northeastern NY. I only use Kerosene in mine, If you have been using Diesel, add a couple gallons of Kerosene in the tank, and slosh it around in case it has settled out. I also put in about 1/2 Quart of Diesel Fuel Conditioner, as I know that it has water in it from Condensation. You can tell if you have water in the fuel, it will be running good, then it will miss fire, with a cloud of smoke than run again.
As far as buying Diesel Fuel Conditioner, I was in Wal Mart yesterday, an see that they sell the Same stuff I was buying at the Auto Parts Store, for 25% less than I was Paying.