"Hi! Can you walk me through your poster?"
I always dread saying these words because I don't know if the poster presenter is going to talk for 5 minutes or 30 seconds. I prefer the concise 30-second response. This way, I have time to ask questions about the things I'm curious about, which in turn, allows for a (hopefully) meaningful discussion with the presenter. To serve my own interests, here are my preferences for presenting a poster...
1. In advance of the presentation, have prepared a short description of your study that takes no more than 30 seconds to talk through
2. Practice giving your short description before the presentation; or at least rehearse the description in your head a few times while you are waiting for people to show-up to your poster
3. After you give your 30-second description, wait for your audience to respond
4. If your audience has questions and a discussion begins, make sure to learn about your audience (e.g., who are they and what do they do) so that you can tailor your responses to their interests/motivations
5. If you find yourself rambling on, simply stop and acknowledge that you are talking too much (e.g., "Sorry, I'm talking so much. I can get a little passionate about this topic.")