Speak with Pathstalker Kariel - the Rogue class trainer - inside the Sunspire on Sunstrider Isle.
As you advance within your class, you will want to take advantage of the training that your class trainer can provide you. For young rogues here on Sunstrider Isle, your trainer is Pathstalker Kariel. Speak with Kariel and see what training he has available for you. The things he will teach do have a cost, so bring some coin with you.
Kariel - as with all the trainers on Sunstrider Isle - is inside the Sunspire on the lower level.
I've heard your name whispered from the shadows, <name>. It's said that you're looking for someone experienced to show you the ropes - someone like me. I can do that, but it'll cost you a small cut of your take every time I've got something to teach you. So yes, I will train you in what it means to be a rogue.
But remember, if you ever get caught stealing something, this conversation never took place. Now get out there and show me what you're made of!