She was mortified. New to the position and new to the office, she wanted to make a good impression on her colleagues as well as the customers, and show that she was friendly, approachable and willing to be of help.  

But when approached by a co-worker while in deep concentration on a project, she did what a lot of people do ... she looked up with that unconscious reaction to an interruption written all over her face. The frown, the "I'm thinking of something else", the "hrrmmph" expression.  

Fortunately, she caught herself in the act and had the opportunity to smooth out her face and switch gears before it was noticed. However, so often when this happens the person receiving "the look" may interpret it as anger, frustration, or irritation at the interruption and at them, when actually, the person giving "the look" is none of those things and is thinking of something else entirely.  

So how do you deal with interruptions?

1.  Be aware that you need to switch gears before you lift your head and face the person approaching you; your expression speaks volumes! Again, while you may be thinking of the project you are dealing with, the person in front of you may think your frown is aimed at him.

2.  Immediately offer a greeting and a smile to the person. Think friendly ... approachable.

3. If you need a moment, say so, but do it in a friendly, non-gruff manner. You sense the person standing next to you ... perhaps use your finger to mark your place as you finish up, (the person will note your action) saying "Give me just a moment; I'll be right with you." Then, as you finish and look up with a smile, "Thank you! Now, what can I do for you ..." People can tell that you are busy but they want to know they have been seen.