Besides the comments above, I can offer advice on what not to do....based on some unfortuate issues with externs we've had in the past.
Be willing to do whatever you're asked. And if you're not asked, offer to help.
Stay out of the office politics. If you unwittingly place yourself in the middle of an unpopular issue, you might not be asked back. If anyone tries to suck you in....act noncommittal and keep quiet.
Dress appropriately; conservative is best, or at least follow the lead of your manager.
Don't smoke. This is a big one. Even if you take a break during your assigned lunch or breaktime and go out for a cigarette, you advertise that you are a smoker....something that some managers (me included) don't want to have to police.
Ask questions when appropriate. Everyone's busy and might view your over-enthusiasm as peskiness. Unfortunately, externships can be viewed by exisiting staff as 'having to babysit'. A good manager won't allow that attitude, but it does exist.
Be prepared to do the 'scut' work. You're not going to be offered the corner office, but at least you'll get an idea of the kinds of things that bog the rest of the team down. Think of solutions and workarounds to make things easier. Your suggestions might impress someone.
Don't ask questions of the regular staff that are none of your business.....'how much do you make?' for example. Your questions should be entirely work related.
Admit if you're in over your head, or if you don't understand something. Nothing burns your bridges faster than the staff having to clean up after you when your externship is over.
Pay attention to your environment in regards to the level of office noise and atmosphere. Remember, coders are often head-down and deep in thought. Your running commentary of your two-year-old's birthday party last week might not be what everyone wants to hear about.
Shut off your cell phone, or put it on vibrate. If you take a non-work related call, leave the area. Any personal details about your life are best kept to yourself. You wouldn't want to share anything that might suggest you have personal problems that a new employer might not want to have to deal with.
I don't mean to suggest that every extern is as clueless as the examples above, but you'd be surprised what's out there! (or maybe not). Everyone wants to make a good impression, but sometimes we aren't realistic about the things we do that might hurt our chances.
Pam Brooks, MHA, CPC, PCS, COC
Dover, NH 03820
If you can dream it, you can do it. Walt Disney