Speak with Summoner Teli'Larien - the Warlock 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 warlocks here on Sunstrider Isle, your trainer is Summoner Teli'Larien. Speak with Summoner Teli'Larien and see what training he has available for you. The things he will teach do have a cost, so bring some coin with you.
Your trainer - as with all the trainers on Sunstrider Isle - is inside the Sunspire on the lower level.
<name> - your name has passed my ears as one seeking out a master in the ways of the <class>. You look capable enough, but I seek more than just looks from my students. You must be ready to delve where others fear to look to gain your power. I will teach you, but I will not tolerate failure.
There will be monetary costs associated with your training, but you should be more concerned with the cost your mind is willing to make. If you are ready, we shall begin.