If you're just starting Battle of the Immortals, there are things that will help you out with levelling.
First off, you'll need to download it. You can do this at http://boi.perfectworld.com/download. Download it, install it, then create an account and log in.
After you make the account, create a character. Now, it doesn't matter which because you won't be using this one much. I suggest making a heretic, though, because you WILL be getting this to level 30. After you make the character, you'll want to log in, get the induction ID off of it. There's a button near the bottom right of the screen. I haven't been on in a while, so I forgot a bit about it, but it's not hard to find. Copy it to your clipboard, log off of this character, and make a new one. This new one will be your main, so pick a class you'll like. There are five classes on this game as of now, I'll offer a brief description of each here:
Heretic: The healer class. Has buffs to increase stats. Wisdom is their stat
Champion: The tanking class. Has skills to take and hold a mob's attention. Vit is their stat.
Berzerker: DD class. Has skills to increase attack speed. Physical damage. Str is their stat.
Slayer: DD class. High crit rate. Physical damage. Dex is their stat.
Magus: DD class. High magic attack and nice AOE potential. Magic damage. Int is their stat.
Now, once you have chosen your class, you'll want to level up both of your characters to level 30. At that point, multi client and do Knight's Jail. Accept the quest from Medea, I believe. You'll get a Common Mount Token from it after you kill Hannibal, who is the last boss in the Knight's Jail instance. You also get five tokens from it which go towards getting special armour sets that give pretty good stats for their price. You can do this instance up to five times a day.
You always want to do your quests. They give really nice rewards.
This is all you really need to know to really level. Quest, induction, etc.