It is easy to keep brown sugar from getting hard. What you should do is store it in a clean, dry, and air-tight container. The reason brown sugar becomes hard is the loss of its moisture due to exposure to the air. Keeping the container tightly closed when not in use will lock the moisture inside and keep the sugar soft. Even a resealable plastic bag can do the trick, if you don’t have a tightly closed container around. Just make sure to keep it locked until the time to use the sugar. Another important thing is to only use a clean and dry spoon or scoop when taking the sugar out. Any liquid or excessive moisture inside your jar of sugar will ruin it as well.