First, ready the jars, lids and screw bands. Jars, whether new or previously used, should be free of chips and scratches. New lids must be used for each batch, though screw bands, if in good condition, can be reused. Wash the jars, lids and bands well in hot soapy water, either by hand or in a dishwasher. Place the lids in a small saucepan with water to cover, bring to a simmer (180°F/82°C) and maintain the simmer until you are ready to use them. Avoid boiling the lids, or you may compromise the seal.
If the recipe processing time is more than 10 minutes, the jars need only be washed before use, since sterilization will occur during processing. If the recipe processing time is 10 minutes or less, however, the jars must be sterilized in the boiling-water canner before they are filled. To sterilize them, fill the canner pot two-thirds full of hot water. Fill the jars with hot water and, using a rubber-coated jar lifter, lower the jars, one at a time, onto the rack in the water-filled pot, making sure they are covered by at least 1 inch of water. Bring the water to a boil over high heat and boil for 10 minutes. Turn off the heat and leave the jars in the hot water. Remove them with the jar lifter and dry them as needed.
Always keep the jars warm until you are ready to fill them to ensure that they don't break when a hot mixture is added and that they seal properly. If you have cleaned the jars in a dishwasher and they don't need sterilization, leave them in the dishwasher with the door closed, removing them, one at a time, as needed. If you have sterilized them in the canner pot, leave them in the hot water until needed. You can also keep just-washed jars warm by immersing them in a large pan filled with boiling water and then turning off the heat, or by slipping them into a low-temperature oven.