I am level 10 on character barbarian. People said I had to be at level 10 to defeat the Skeleton king. I will probably some tonight and see if I can finally beat him. Is there any helpful hints to kill him?
The easiest way would to join a randoms game. On single player, the boss and all the minion are focused on you and you alone. So they can easily gang up on you. This is not that much of a problem with more people in the game.
If you can't, or wont play multiplayer, I would just suggest you bump the difficulty down to easy for that fight.