Before interviews, you should review the most common "tell me about a time when you..." questions, and come up with good answers. When you answer them, ALWAYS follow the STAR approach (Situatino, Task, Action, Result). The most important part is result -- you can tell a great story, but if you don't tell them how it ended up saving the company money, or how ie ended up saving your relationship with your boss, or whatever, it's far less compelling.
Also, there's nothing technically wrong with making up answers to those questions, technically. It's probably immoral, but eh?