Tip: Canning Jar Selection, Preparation and Use
Examine jars and discard those with nicks, cracks and rough edges. These defects will not permit an airtight seal on the jar and food spoilage will result. All canning jars should be washed in soapy water, rinsed well and then kept hot before use. This could be done in the dishwasher or by placing the jars in the water that is heating in your canner. The jars need to be kept hot to prevent breakage when they're filled with a hot product and placed in the canner for processing.
Jars processed in a boiling water bath canner for 10 minutes or more or in a pressure cooker will be sterilized during processing. Jars that will be filled with food and processed for less than 10 minutes in a boiling water bath canner need to be sterilized by boiling them for 10 minutes. NOTE: If you are at an altitude of 1000 feet or more, boil an additional minute for each 1000 feet of additional altitude.
Tip is from Fagor's home canning cookbook