Okay, then: should you plan to memorize the story and walk in without copy to read from?
Not that, either.
Obviously, you want to practice some, but not to the point where your own words give you a dreary feeling of familiarity. And you want to set yourself up so that reading is as easy as possible. For me, that means printing out a copy of whatever I’m reading in larger than usual type (or, if you’re reading from your laptop or tablet or, ebook, blow the image up a little larger than usual). This is simply good sense: who knows what the light is going to be like where you’re reading? What if you find yourself squinting or bending over your story trying to read it? Why make life more difficult than it needs to be. If I’m doing a reading I generally try to keep the type at 14-16 points.
Then there’s timing. It is pretty much certain that when you’re reading you’re going to speed up. Adrenaline will do that to you. Fear that you won’t be able to read everything you’d meant to read in the time you have can be a factor too. But trust me: no good comes from speeding up. So you read your work aloud to get a sense of how long it takes to read… and then add 10%. Practice reading at what will feel like a glacial pace: if you record and play it back you’ll note that you don’t sound slow–you sound pretty normal. So rehearsing will get you comfortable with the pacing that works for you and your listeners.
Another thing–which may be peculiar to me, but I doubt it–is that in reading your piece aloud you may find infelicities, places where another word would work better, things you might want to change. Reading the text aloud before you have to do it in front of an audience means that you can catch those things, and be less prone to whip out a pencil in the middle of your reading and annotate.
You rehearse your reading for your own sake. You rehearse your reading for the sake of your audience. Cause you want your audience to love your work and want more of it.