Very simple! I collect and use jars that are squat, not too big, have a large opening (easy for pouring into) and have a little bit of decoration if possible. I don’t tend to use jars that have previously had a very aromatic or spicy substance in them as this can permeate the lid and affect the taste of your jam if using later. However if making a spicy chutney then this would be ok.
If someone has given you a lovely expensive jam….that’s the jar to keep and recycle as they are often a good quality glass and have been made for jams. Metal lids are better too if possible.
Wash any jars ( and a glass pyrex pouring jug for filling your jars) in warm water and detergent. Rinse well and place wet onto an oven tray. Place in the oven on approx. 150 degrees and warm until all the water has disappeared and the glass feels hot! Turn off oven but leave jars and jug in oven until ready to use.