Has confidence, but not over-confident. Obviously knowledgeable about the work to be done, but not vaunting.

Someone that looks like they could potentially handle tasks on their own, be a good apprentice, and that you won't have to spend time arguing with to get them to do something simple.

Basically an intern should be a humble worker that gets the job done.

Interns come to work the first day feeling like they will be valued and a part of the team, but are hired because they are seen as cheap labor by the employer, and once they get there are usually not treated as a "real" employee. So they need to get work done, but in a way that doesn't rock the boat.