Call 911. While waiting for medical help, follow these steps:
Look first. Don't touch. The person may still be in contact with the electrical source. Touching the person may pass the current through you.Turn off the source of electricity, if possible. If not, move the source away from you and the person, using a nonconducting object made of cardboard, plastic or wood.Check for signs of circulation (breathing, coughing or movement). If absent, begin cardiopulmonary resuscitation (CPR) immediately.Prevent shock. Lay the person down and, if possible, position the head slightly lower than the trunk, with the legs elevated.After coming into contact with electricity, the person should see a doctor to check for internal injuries, even if he or she has no obvious signs or symptoms.
Don't touch the person with your bare hands if he or she is still in contact with the electrical current.Don't get near high-voltage wires until the power is turned off. Stay at least 20 feet away — farther if wires are jumping and sparking.Don't move a person with an electrical injury unless the person is in immediate danger.
If you live in the US, call 911 if you notice serious injuries, usually the result of being electrocuted are severe burns and heart failure, if he's suffering from no burns and seems alright, he probably is...
Jumangimon definitely has the best answer, but I'd like to add the following. I'm an electrician so I know a thing or two about a thing or two. If the person is on a ladder, kick it down! falling 6 or even 10 feet is better than being "locked" on to a live wire. at least 8 times out of 10, the source or breaker panel is not a realistic option. It's probably located relatively far away. I know that if I was being electrocuted I'd rather be tackled or hit with a non-conductive object than boil from the inside. For the guy who got tasered, yes a taser gun operates with 50,000 volts but the amperage is non-existant. on a typical 120 volt cct the amperage depends on what device is drawing power, how much it's drawing and your resistance. It's more the amps that kill you than the voltage. however remember this. One Amp at One Volt has the potential to kill a human