"Tell me about your last three positions?"
This type of question is generally asked by lazy interviewers who want to hear you talk for a while. A better question would be to separate the three positions and ask them one by one. But some people will ask this question, so you should definitely prepare for it. You can use this as your advantage. If you don't have many good things to say about your second position, you can briefly comment on it and spend more time talking about the other two positions. I'll give an example in the long answer, but here are some short answers first.
Short Answers
"I've only had one position. In my last position, I worked as a marketing analyst for South American markets. I worked closely with partners in Chile and Argentina."
"I've only held two different positions. In my first job, I was a lab manager for ABC Software company. I monitored 50 computers and performed diagnostics regularly. In my last position, I was a network engineer fixing network problems and trouble shooting bottlenecks."
"I worked as a translator for the King County court house. Afterwards, I worked as a translator for hospitals. My last position was translating help documents for a software company."
Long Answer
"The first position I held was working at Radio Shack as a salesman. I learned a great deal about retail stores, about sales and working with customers, and became more independent. I thought I learned a great deal and enjoyed my work, but I wanted to experience different types of work. So I started working for Verizon. I had an office job and did a variety of different tasks such as planning, data entry, and organizing projects. I learned a little about the office setting, but I wanted to get back into sales. So I was given an opportunity to sell cell phones for Verizon at a retail store. I used my past sales experience and worked hard becoming one of the top sales person three years in a row. I've been there ever since."
I haven't worked at three different positions, so I just made one up. The question is pretty general, so the answer is pretty general. It does emphasize sales skill and coming back to the type of work that this person enjoys. But you should think of something that is related to the position you are interviewing for. Only thing you should be concerned about it clearly explaining your past three positions, what you learned there, and if you did something notable, include that as well.