Mistakes commonly made when pressure canning include:

• Taking “short cuts.” Recommended preparation and processing instructions should always be followed.
• Using jars not specifically designed for home canning. Commercial glass jars with screw-on lids should not be used when canning.
• Using outdated canning books or instructions. Updated (within the past 10 years) canning books and instructions should be used.
• Using untested recipes. Canning recipes should always be sought from a reliable source such as your local extension office

For more, go here.   Thanks to Extension Service, USDA.