What do you plan on doing in the instance? Tanking, DPS assist, or healing? If you're tanking or doing DPS you're probably going to want to think about offensive gear; healing is more defensive. Thott has a Slave Pens article that people have contributed to (I haven't read it, I just gave it a glance so I don't know what's actually on there). There are Slave Pens guides on the interweb as well on a couple instancing guide sites as well.