PKing stands for player killing. This only said when killing in the wilderness. The wilderness, or wildy can be a dangerous place if unprepared. Obviously don't take anything of value in the wildy with out planing on losing it. The wildy can also be a place of fun, if you are the one doing the killing.
Green dragons are a great place to pk. Sites include lvl 11 wildy to the wesr, 22 wildy central, and 23 wildy very east. Most dragon killers are 3 itemers, so you wont get anything good besides free dragon bones. If you are looking for some fun and you can't find anyone to kill, green dragons are a great spot. Don't forget a dragonfire shield!
RC pking is killing at the zamorak mage (lvl 6 wildy North of edgeville) that teleports you to the abyss. Rune crafters are skulled, and almost never have food. They also wear glory amulets, so they are decent kills. You want to either teleblock and entangle them, and dds special them very fast, or blitz or barrage them and then dds special them. The down side of this pking is that it is seen as a cheap way to kill.
Mage bank is one of the most dangerous places to pk. It is NOT multicombat so going with your friends as protection won't help too much. Normally a level 110-126 is waiting at the teleport with teleblock. Although this can also be a good place to pk becuase the pkers here ussually have full barrows, a whip, and more on them.
Level 40 pking... My personal favorite.... I love this kind of pking because it is always multicombat, so you and your friends can all have fun and you get a lot of level 80s - 100s that are normally skulled and have decent items. It does take a while to find a good kill but it can be worth it. In this type of pking you go around and around to the rune rocks, to the demonic ruins, and then to the rouges camp. If you find no one, you can keep looking or switch worlds. The only downside is that on the rare occasion you see a clan around level 40 or higher and multicombat, and you are toast....
Mage: if pking in under level 20 ,use regular spell list and teleblock along with entangle. Carry a dds with you just incase and use a god spell. Make sure you bring a super strength with you too.
If you have done desert treasure, pking with ancients is the best route. Always use freeze spells when on ancients. Blitz or barrage is best, Still carry a dds with you.
Ranger: Rangers are the best for pking budget wise. All a ranger needs is a magic shortbow and full black d hide. A dds is not required for rangers because you will drown your spec with your bow anyways. Higher level rangers may choose to go with a crystal bow when pking which will greatly increase damage.
Melee: For pking with melee, you should go in full black dragon hide, dds, and a dragon scimi or a whip. Do NOT bring rune with you because you will get killed very fast my mages. If you want to go on the cheap side simply use a dds and monk robes. A super set would be a very good idea.
For free world pking swordfish are your best bet. Heal 14 each.
If you want some effective and cheap food, go for monkfish. Heal 16 each.
If you are serious about pking go for sharks. Heal 20 each.
Even more serious pkers can use cooked tuna potatoes... These heal 22 each!