Relief pitching in high school

from what my coaches have told me so far, my job as a pitcher this year will manly be relief work behind our three or four senior starters. this is gonna be something pretty new to me. any good advice out there?? also, since i lack experience, i really week on the strategy part of pitch. like how to set a hitter up and what pitches to throw when.
if it helps at all, i throw a two seem and four seem fastball,
a decent circle change, and a curve that is in progress. thanks for any advice you can throw out there.

my bad, for posting this in the wrong section