Mash the ripest fruit you can find
If you’re going to experiment, start out with a small amount, about 2 cups of crushed fruit. If you want to make a larger batch, double this. When trying to figure out how much fruit you’ll need, use this rule of thumb: 1 pound of fruit without pits or 1 ½ pounds of fruit with pits will give you about 2 cups crushed fruit.
Add lemon juice (about a tablespoon per 2 cups of crushed fruit) to low acid fruit like peaches and apricots, both for flavor and to help the jam set.
Sugar or other sweetener
When using Pomona’s, mix the sugar with the fruit. For Ball, combine the sugar with pectin powder first (for two cups of fresh fruit, you’ll need just half of the 1.59-ounce packet) and then add it to the fruit.
Add pectin to fruit and stir well
Pomona’s pectin comes with a packet of calcium powder. Prepare it according to the instructions and add a teaspoon at a time of the calcium water. Stick to the very low end of their recommended amounts if you don’t want a very firm jam. The jam will continue to set a little more after stirring.