Friends are a version of extended family to most people, so when they hurt, you hurt. You want to be able to help them however you can and get them in good spirits again. Especially once they've broken up with their significant other.
Guy friends will tend to go out and about on the town, show him all the girls he could have, and how much fun the single life can be that he's been missing out on. Girls, on the other hand, will sit together and talk, maybe have a few drinks, and reminisce on the relationship, regrets, hopes, wishes, dreams, etc. Each react how society tells them they should, but they do what they need to do to cheer their friend up.
Everyone has different reactions to a breakup depending on how long the couple was together, why and how the breakup occurred, and, if they're even on speaking terms or not. Sometimes breakups can be for the best interest of both parties, but more than likely, one wants it more than the other. Sometimes things can be civil, and sometimes not.
There are several things friends can do for each other when one of them is dealing with a breakup. Listen. Sit and listen. That's all you will need to do. Do not offer opinions, just in case this is a temporary situation, just to be on the safe side. You don't want to cause unnecessary arguments down the road. Let your silence speak volumes of how much you really care.
Another tactic would be to encourage your friend to express their feelings. This can help deflate anger and move past grief to get to a place where they might feel relieved in some way. You can also help her reaffirm her identity separate of hers within the former relationship. Do not let them shut down and become just hopeless and depressed, insecure, or even to the point they let it really affect their life (for example, missing out on school, work, and other important aspects of their life).
Be sure you are available for your friend to make time for them. When relationships end, schedules change as well. All the time previously devoted towards the former significant other is gone, and they will be left with wide open spaces in their schedules. That leaves time for a lot of thinking, analyzing, and reminiscing about memories that will probably just get them more upset.
Participate in a hobby or activity that your friend used to do before or less when the relationship took off. Reignite that passion they used to have and help her follow through with it. And, no matter how much you're there for your friend, sometimes you'll need backup. Bring along other mutual friends of yours, even new people that you know would be a great help in cheering her up and getting her motiviated. It always helps to make new friends to fill the void your friend must be feeling now.
Getting fresh air and exercise is always a plus, although it takes energy and motivation to follow through with it, even when you are not dealing with heartbreak. Improve your friend's mood by get them moving, go on a hike, even for a simple walk, anything will help. The endorphins released from exercise can help stimulate the brain and produce feelings of euphoria. Release the body's natural antidepressants by starting or initiating a workout routine with your friend. She or he will love you for it later and may even pull ahead of you!
Work with your friend on the positives and negatives of breaking up with this person was. This will take some time and is not something that can be figured out within an hour, but will take some work. Everything happens for a reason, and this relationship had its purpose(s). What were those, and how can you improve individually from here on out? Personal growth is always important and can be done each and every day.