One method of softening brown sugar includes sealing it in a bag with a slice of bread or a few slices of apple for a day. Another method is microwaving it in a bowl for about 20 seconds with a damp paper towel on top.
The first method is useful when you know in advance that you will be using brown sugar, while the second method is good for a quick softening. The bread and apples will be dried out after a day because most of the moisture will have moved to the brown sugar. The apples may add a nice fall flavor to the brown sugar. While microwaving, it is important to not overheat the sugar, as it can turn gooey.