This is a fantastic site for how to make a good informative poster. It's worth the read and not too long either.
I have looked at a few sites and they all say some pretty similar things;
name and tital should be first, your tital should be your punchline
condense your information
you have roughly 11 seconds to grab your audience, so use your tital well
don't put too much information on the poster, if its too busy no one will bother to look at it
and the text size needs to be able to be read from 6 feet away.
These are only a few of the criteria but they are pretty helpful.