I can tell you that you should explore the roots of speculative fiction and what it means. For example, here are the novels that we read in my class(which was admittedly a college-level course).
Pilgrim's Progress (John Bunyan)
The Invisible Man (Wells)
The Hobbit (Tolkien) - Whatever you do, don't try to do so thoroughly. The Hobbit alone is a lot of material.
The Neverending Story (Michael Ende) - HIGHLY recommend this one.
Divine Right's Trip (Gurney Norman) - This was an excellent book that I still reference today, but is probably the first one on this list that I'd drop.
We also covered numerous short stories. A few of the more memorable ones:
The Cold Equations (Tom Godwin) - Excellent, if dated. there's a film of it, as well, but it added a lot of side material.
The Celestial Railroad (Hawthorne) - Highly recommended after Pilgrim's Progress.
The Last Question (Asimov) - Required reading.
Heinlein is also an excellent choice, though we didn't cover it in my class.