Reusing jam jars keeps costs down and is much better for the environment than using new jars.
First off it's important to carefully check the jars for cracks or chips, don't be tempted to use these as they can be hiding places for bacteria. Put these to another use such as making hanging tea light holders.
Give the jars a good wash in very hot soapy water, paying special care to the screw threads as bits can often get stuck here.
Place the jars upside down in a baking tray on a clean tea towel then put it the oven to dry and sterilise, set the oven to about 100 °C (212 °F).
Aim to put the jars in the oven about half an hour before they are needed, this way they can be taken out warm and quickly filled with hot jam or chutney.
Reusing lids is fine, make sure they have a plastic lining (most do if they have been used for food jars) and are undamaged, then clean them well in hot soapy water.
Sterilised by boiling in water for 10 minutes.
If using a jam funnel, sterilise this at he same time as the lids.
When ready to use the jars, take out of the oven and use a clean tea towel to turn the right way up. A good tip is to keep them in the baking tray while filling as this minimises mess from any spillages.