Percy has several mentors who attempt to help him to adjust to life as a demigod.  Foremost, Mr. Brunner, who later reveals his real identity as Chiron, encourages Percy to focus on Greek mythology at the very beginning of the novel:

"'You must learn the answers to my questions,' Mr. Brunner told me.

'About the Titans?'

'About real life.  And how your studies apply to it. [...] What you learn from me,' he said, 'is vitally important.  I expect you to treat it as such.  I will accept only the best from you, Percy Jackson.'

I wanted to get angry, this guy pushed me so hard" (7).

Chiron pushes Percy to realize his full potential, but he also aids him in other ways as well.  Chiron guides Percy around Camp Half-blood, explaining to him the history, layout, and organization of the camp.  He looks out for Percy's needs and provides him with a sword to defeat Mrs. Dodds.  More importantly, Chiron has a long history of being a "trainer of heroes" dating back to Hercules.  He was granted a wish to be a teacher of heroes for as long as humanity needed him, and Percy is his next project. 

Another lesser mentor to Percy is Luke from the Hermes cabin.  Like Chiron, he also advises Percy on his new life as a demi-god, even loaning Percy his winged shoes for Percy's quest.  Unlike Chiron, Luke had a definite ulterior motive in aiding Percy, whom he ultimately wanted to take the blame for the theft of the Master Bolt.