There isn't a whole lot that you can do, but the first thing you should do is call 911. After which you can proceed to do the following.

1. Don't touch the person until you're sure that they're no longer in contact with the source of electricity. You don't want to get shocked and be in the same position they're in.

2. Turn off the source of the electricity immediately and if you can't then move the person or the part of the person that's in contact with the electricity away from it using a non-conductive material like wood or plastic

3. Check for signs of life, if the person isn't breathing then administer CPR immediately

4. Prevent shock. Lay the person down and, if possible, position the head slightly lower than the trunk, with the legs elevated

Please make sure that you don't touch the person with your bare hands, the human body is a good conductor of electricity, you'll get shocked if the person is still in contact with the source of electricity and try not to move the person until the paramedics get there, only move them if absolutely necessary!!!