Introduce a question and answer, then instruct students to ask the question to their neighbour. They then answer the question and ask the same question to their neighbour and so on.
Keep feeding the rows questions that get more and more difficult. You can then make it a competition, so the first row with the last person in it to have answered the last question wins. This is good for practising Q & A and it means that everybody is asked all of the questions without getting bored.
If you want to, you can have the questions on slips of paper and they get passed back in the row.