I've been tempted plenty of times to give brief answers and drop the formalities. While sometimes it gets busy and there isn't time, I feel that overlooking friendly formalities altogether is a mistake.
Live Help is a major marketing tool for Linden Lab. Often time it's one of the first contacts new residents have with other residents. It can affect whether or not they love SL or whether they get frustrated and leave.
Knowing this, I recommend:
1. Say "Hello".
Don't just provide the answer. Say "hi". Click the profile button. If they're new, welcome them to second life. Not only does this make them feel more welcome, but if they have a problem that can't be solved, at least they will feel as if people are there to try and support them. In addition, it signals to other Live Helpers that you are handling the Live Help question, and you don't get 4 people all posting the same answer.
2. If they're really frustrated, teleport to them.
It's amazing how much your presence can make them feel better, which will keep them happy and able to better answer your questions to figure out their problem.
3. If it's a griefer problem, don't put yourself in the middle.
Advise the person to be calm, not swear, and to be nice to the griefer. In the end, that will make their Abuse Report all that more effective when the chat log is included. I have informed griefers that they can be reported if they continue doing what they're doing, but I make sure I witness it myself and I don't go by either person's word alone.
4. Above all, keep a calm and kind tone.
I don't think any of the current Live Helpers have this problem from what I've seen. But occaisionally a person looking for help can be a real jerk, and volunteers in the past have slipped. Be apologetic if you can't help them. If there's a delay, let them know. If you try and can't solve the problem and they are unsatisfied, 9 times out of 10 a "sorry, I don't know what more I can do" with a direction to contact Support will keep the resident satisfied.
5. Don't leave early!
Leave your window open until you're sure the person is helped. (Usually the person saying "thanks!" and closing their session is a good sign.) I also recommend a simple, "Is there anything else we can help you with?" or "If you have any more questions, don't hesitate to ask Live Help again!"
Also, as with saying hello, it doesn't hurt to say "good bye" or "good luck" or "have a nice day".
/206/26/51882/1.html - check out Pituca's response. This is NOT what you want to leave as an impression on new players.