What are some ways I could cheer up my friend that just got dumped?
Im sorry your friend recently got dumped.  I would ask them if they want to talk about it, or be distracted from it.  If they want to talk about it, I would find a quiet place and a warm beverage and listen.  If they want to be distracted from it, I would find a local favorite bar or activity that your friend enjoys, and take them there.  Call as many of your joint friends as possible, and provide ample supply of distractions for your friend.