Leave enough slack in the pigtail so that it lies flag against the comm. You don't want the wire to stretch tightly to the comm tab. Mark the end of wire. If you break a wire now it is trash time. Use as little solder as you can.
Silver solder is the strongest.
Be very careful of the heat. You can damage a comm by leaving the soldering pencil on it too long. Now is not the time to learn how to solder. If you are new to this, practice first on some scrap printer circuit board material. The wires should lie flat on the comm as they go to the tab.