To sterilise the jars in hot soapy water. Don’t dry them with a tea towel. Position them on a tray (for ease of moving them) and place in a warm oven set at 140℃ ( 120℃ fan)/275 F? Gas mark 1 to dry completely. If you’re using kilner jars, boil the rubber seals as dry heat can damage them.
Avoid re-using jars that have previously contained tomato based sauces or spicy food. Even when thoroughly washed the original aroma will still linger.