Communication and Fast Turnaround
To try testing on a Scrum team, learn about Scrum and find out about the motivation behind the methodology. Realize that you will have to be proactive in getting test information—requirements won't necessarily be handed to you. Your teammates will expect quick feedback, so look at testing techniques that will help you to get that information quickly. You can rely on your skills of observation and inference to apply different testing techniques on a product or feature for which you don't have a specification. This is a valuable testing skill, and works well for gathering useful test information. It's also a powerful way of uncovering hidden assumptions in a product. For more information on testing without a map and to execute tests quickly, check out James Bach's Rapid Software Testing course (also taught by Michael Bolton). Focus on testing according to risk, and learn to plan on the fly. Above all, communicate and ask questions. If Scrum item lists are too vague for you to test, ask for clarification and work with your teammates. A more testable design is a more coherent design, so they'll thank you for it. Scrum teams can be a rewarding place for a tester, so give it a try.