Lisa Crispin and Janet Gregory have written extensively about this. They have written here and have written a book about it. (No, they didn't pay me to say this! I do know them and like them :-)
Their book is "Agile Testing: A Practical Guide for Testers and Agile Teams".
Elisabeth Hendrickson is another agile test author whom I highly recommend. She has a new book out, "Explore It!"
My guidelines: Automate the feature testing so you can explore around the features. As with all advice, your mileage will vary.
Start with these suggestions and you will be on the right track.
Agile is one of those activities where the more you do it, the more it just makes sense. And once you start winning with agile, the “A-ha!” moments will come fast and furious. With this in mind, I decided to ask members of the Ascendle team – all experienced agile practitioners – to look back at their own A-ha! moments while using Scrum to manage their client projects. Here are some of the agile lessons learned they shared.
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