Playerkilling is quite a different experience than running experience or even tackling a solitary mob. You are not worried about conserving mana, blow it all as quickly as possible, then retreat and regen. That is, of course, unless you plan on fighting multiple enemies.
Players are unpredictable, they don't behave like mobs. They have a vast repertoire of spells, of which you do not know all of them. Example, the djinni mage casts fireball, so ice shield would be the defensive spell of choice. A player however, might know shocking grasp, fireball and cone of cold.
Your eq- No certain eq type works best in a pk match. Since you rarely know what you're up against it's not a good idea to plan on just changing eq. A good balance between hitting ability and armor class is important, and if you've got a good enough set, mage gear pays off. Players generally have lower hitrolls than mobs, so figure that in. They are, however, capable of dishing out a lot more punishment with spells. All the defensive spells are valuable, especially stone skin and sanctuary.
There are only two true types of pk's. Naked, and comlpetely non- restricted. Both are the only true ways to measure a character. If someone ever says, "I'll fight you but no invis" simply because they don't have invis or detect invis and you do...then they are depriving you of a facet of your character.
Also, DISPEL THEM!!! It can possibly increase your damage-dealing capability tenfold. If they've got all the defensive spells up and you can only get a few it's still better than dealing with a completely spelled up opponent. Disarming is good too, pick up their weapon too, and give it back at the end of the fight (see ettiquette). Who's gonna win, the guy with the sunblade or the guy with the knuckles?
There are quite a few features (commonly known as bugs) that most pkers don't know about, use these to your advantage. I can't give you examples, because if I did they'd be fixed, and I don't want that. Try experimenting, a rather inobtrusive example: You can use the "score" command to shut down your opponent.
The most overlooked element of PKing, ettiquette is the most important. You might think I'm hypocritical by saying "take every advantage" and "be courteous." There's a world of difference between being pragmatic and being a turd. Don't do things to people that they have no form of retaliation, such as dispelling or noxing people in recall. Also, it's not a good idea to do things to someone that will cause trouble after the fight, such as disarming and saccing their weapon, or stealing something from them.
The Dark Forest East
Or see what Firebird thinks of the PK scene.