I talked a little bit previously about run/walk intervals. One of the common questions I get is how fast should I run during the run intervals, and nobody ever asks how fast should I walk the walk interval. Well, here's the answer for both!
Conversation pace: During the run interval, you should be able to have a conversation with someone running next to you. In other words, if you are huffing and puffing so much that, if someone were to ask how your weekend was, you could only respond in single word answers, then you're going too fast. You should be able to hold a conversation the whole time (and in fact running with a friend and telling stories to each other is a great way to pass the time).
Walk intervals: The walk interval shouldn't be a slow, casual stroll. It's not racewalking, but even though you are walking you are still training so it should be a brisk walk. Keep your arms moving back and forward and that will help you keep the pace up.