Don't forget 911!!! Activate the emergency system. Many towns especially towns with large bodies of water have Ice rescue teams that practice for these exact emergencies. Being a rescue chief keeping a calm head in these situations goes along way to surviving. Also you don't want to end up in the water trying to save another. Now there are two people who need rescue.
Having a plan is the best way to go. Some cheap ice pics and a 100' length of rope with a large eye splice in the end is a great start. I say have an eye splice because hypothermia starts at the extremities. The person in the water may not be able to grab the rope, but if they can get a hand through the eyesplice and get it up to the elbow you will have a good chance of getting some leverage to pull them out.