Interviewing Advice

[HeavenslilAngel]

So I'm about to be doing an internship, and following that I'll be looking for a job. I feel fairly confident in my interviewing skills, however, the question I hate the most starts with "Tell me about a time when/that you.....". I can never think of an exact response because I'm a pretty go with the flow kind of person in the workplace. So can any of you give me some help on how to answer those types of questions? If your profession is a Hiring Manager or equivalent, can you tell me why these questions are asked and what the interviewer is normally looking for in an answer. Usually my response begins with ummmmm and then a general answer like I can't think of a time I'm usually the type of person who.......
Any help would be appreciated. Thanks!