How to Say No

Cited from 'Learning how to say no' from Lynda.com

It is acceptable to say no when any of the following conditions are met.

1. When the request is not an emergency. 
2. When you are focused and making progress.
3. When you need to meet a deadline.

Smile politely, look at them, and say "Of course I will help you, but not right this minute." Then look at the schedule, and suggest a time you might come see them later in the day.