You can do an independent killer role if you want or you can go caballed and fight the enemies of your cabal. Mindless killer is one role option, idealist(such as Outlander, who have plenty of enemies) is another. Whatever you find more interesting.

Few examples from my two first PK chars, a shapeshifter and an orc:

My first PK-oriented character was Tribunal utility/air shapeshifter(human), and I managed to get fourteen or so kills with the combo(after age dying an explorer Herald), fights mainly against criminals and Ragers. Shifter is good option for PK practice in Hero range, since the actual fighting tactic is simple and the tactic is mainly about in what form to fight. Agantas the shifter started PK as hero. The good thing about shifters is that their fighting abilities aren't gear dependent and they dress for extra hp.

My second PK-character was an orc and the idea was to PK whatever I happen to come upon. I managed to get seven kills or so with the orc, consisting of paladins, assassins and warriors, the tactic being the traditional orcish bash bash bash with axes in hands(though flail has come to fashion among warriors and I wonder if it spreads among orcs as well). My orc Murgh started PK in early 20-range, when he was informed of the location of Alven the paladin, whom he bashed to death after getting decent gear. Orc can be fun, but they can get kicked in the junk pretty badly at times. I had no real problems as Murgh, but my second orc Ghak took a good kick in the junk most of the time when he wasn't ganking. Warriors and orcs tend to gear for damroll.