Develop good technique.
Learn music theory.
Learn to improvise.
Listen to everything and anything you can.
The harp is a fantastic instrument for jazz.
I highly recommend getting a good teacher not just for harp itself but for theory. In the mean time I highly recommend working through Mark Levine’s The Jazz Theory Book.
Also a fun and light introduction to improvisation is Introduction to Improvisation by Deborah Henson-Conant. It’s fun because it comes with a CD of Vamps to improvise over that are very fun and not too hard to work with.
And learn the head and chord progressions of as many Jazz standards as you can.