The Mad King's End The Skeleton king can be a tough opponent, but the first time you fight him he should be no problem at all. If you need to you can always go back to areas and train before fighting him leveling always helps.
Skeleton kings moves:
Bash Attack: Swings his mace at the player
Teleport attack: Moves to where the ghost is swinging his mace
Summon Skeletons: Six skeleton minions are summoned, he usually teleports backwards when using this.
Spinning strike: Spins in 3 circles doing moderate damage, the first being the worst.
There isn't much tactics to fighting him other than beating the heck out of him and his minions. The more people in your game the nicer it is, as long as someone stays alive then everyone can just respawn next to their corpse. Also dont forget to use potions (LB) those are handy!
Good luck and have fun!