If at all possible (and it's not always), watch the earlier speakers and their presentations. At most conferences there's an overlap in themes, and few things are more annoying for an attendee than a speaker who blindly repeats what a previous speaker said.
If you've seen them, you can reference them. You may still be a little repetitive, but use this to reinforce the point - as X said earlier, etc etc; or Y said this earlier, and I disagree because etc etc. You look like you really care about the conference, not just yourself (and other speakers love being name-checked, so it will help you build relationships at that level too).
Lastly, don't be surprised if there's minimal feedback. I often find myself coming off stage on a high, only to have 1-2 people proactively speak to me for the rest of the event. What really amazes me is how many people remember you - I got introduced a few months ago to a business owner in another city, and his first comment to me was "I saw you speak at a conference in 2008 and you gave me some really practical tips on XYX". Blew me away. Good luck!