There's something for everyone in the Graveyard: mages can electrify skulls and Jack'O, archers can pick off zombies and skeletons pretty quickly, and high level warriors tank pretty good in combination with other players against fallens, zombies, and skeletons.
All this makes the graveyard a popular place. One of the things I try to do is when I see a single player fighting a monster I hit that monster once and move on. Why? Simple, generally single players are trying to level and hoping for a drop. You might think helping completely destroy a monster will assist a player, and in some cases this might be true, but mostly it's not - here's why:
As soon as a second player hits a monster, the experience points the monster gives out on death is doubled. Each subsequent hit subtracts from that pool of experience. For example: say a zombie is normally worth 8k experience. You hit that zombie once, now his experience goes up to 16k (minus about 300xp for hitting it). If you don't hit the zombie again, the player who keeps hitting and kills the zombie gets 15,700xp (roughly, these are just example numbers). Now if you start hitting again that number shrinks. The faster and more powerful you are the more experience is taken away from that pool. Now you could be a speed archer and take away a kill, but this is in extremely poor taste.
Techniques like this hold especially true for mages wanting to kill skulls. If you can hit a skull, hit it once and let the mages kill the skulls (they do a much better job anyway).
Now if a group is banding together to speed kill skeletons, zombies and fallens it's a different story. Experience can be racked up pretty quickly with the right group of speed archers, mages and warrior tanks. Normally I find archers and mages get the most experience, but it can be worth a warrior's while to lump in with speed archers and mages (remember to protect them though) because of the sheer speed with which zombies and fallens can go down with the right group. The experience per second just is faster this way, and it's a good way to level. It unfortunately isn't usually a good way to get items (at least not for a slow warrior), the faster, more agile players normally get the drops. So if you're looking for drops, solo, or duo with a helpful player, and remember the one hit experience trick.