Kal Online has a party bonus that rewards groups with a mix of classes. If you usually party with the same people on the same class, this is worth a look. The details below come from the Party Bonus page of the game's English guide.
What a Perfect Party is
The guide says the full job class list is divided into 11 classes. A Perfect Party is a full party of 8 members who all have different classes from one another. Every member must be at least second job, so a mix of second job and third job characters is allowed.
The bonus
As soon as a Perfect Party forms, a "Perfect Party" buff turns on automatically. Members under the buff get an additional 20% experience from monster hunting. The guide states that this can be combined with the Stone of EXP buff. When the party is dismissed, the buff ends.
Class lines the guide lists
The guide's table groups the 11 classes under six lines: Knight, Archer, Magician, Thief, Shaman and Sword Trickster. The Archer page gives that line's tree as Wandering Archer, Apprentice Archer, Imperial Commander, Expert Archer, Imperial General and God of Bow. The full class table is on the Party Bonus page.
Using it in practice
Count your party. If two members share a class, the party does not qualify, because the rule is that all classes must differ. With 8 slots and 11 classes you have some freedom in choosing which classes to leave out. The guide does not say which combinations are best for any particular hunting ground, so I am not going to guess at that here.
If your guild runs Perfect Parties regularly, tell us which classes you group and where you hunt. A shared list of working setups would help new players.
Sources
[1] Kalonline: Party Bonus System (gameagit.com)
[2] [url=http://www.gameagit.com/kalonline/job02]Kalonline: Jobs and Job Tree, Archer (gameagit.com)[/url]