Excellent question, and I'm glad you started this thread.
Sometimes I have the honor of sharing the stage with 3 young women who are the Houghton Sisters. When I watch them performing, I find my cheeks starting to ache because I honestly cannot stop smiling when I watch them sing! They are just delightful, and FULL of stage presence.
They do all the things that have already been mentioned
* Make lots of eye contact with people in all areas of the audience.
* Smile! Not only at the audience, but amongst themselves. I notice that they are animated, lively, and interactive with each other.
* Sharing the music with the audience, as opposed to having some special talent that is being flaunted at the audience .
* Being human. I have found that the audience really likes that. I'm not a professional by any means, and when my band performs and we start a tune, and don't really start well, we feels OK stopping and saying something like, "How about if we try again, and this time all play the same song at the same time?" I have found that audience appreciate this accessibility as opposed to being put off by "how unprofessional" it is.
One thing that hasn't been mentioned yet that has to do with stage presence is acknowledging the audience's applause. It may feel awkward at first, but looking at your audience with a nice smile and a solid, "thanks" is really important.
I'm looking forward to more advise, as this is a topic I have lots of room for growth.