What are the best practices in Agile requirement??

Transparency is the key for and Agile based project be it on the part of management or on the part of developers.

Else we can never utlise the full power of Agile.

According to me, in every requirements approach there must be active participation of stakeholders,  There are two issues that need to be addressed to enable this practice like, the availability of project stakeholders to provide requirements and then their and teams willingness to actively model together. And if your project stakeholders are unable or unwilling to participate then that is a clear indication that your project does not have the internal support that it needs to succeed, therefore you should either address the problem or cancel your project to minimize your losses.   Active Stakeholder Participation  is a core practice of Agile Modeling.

1. Stakeholders actively participate
2. Adopt inclusive models
3. Take a breadth-first approach
4. Model storm details just in time (JIT)
5. Treat requirements like a prioritized stack
6. Prefer executable requirements over static documentation
7. Your goal is to implement requirements, not document them
8. Recognize that you have a wide range of stakeholders
9. Create platform independent requirements to a point
10. Smaller is better
11. Question traceability
12. Explain the techniques
13. Adopt stakeholder terminology
14. Keep it fun
15. Obtain management support
16. Turn stakeholders into developers

Yes smitha has made a very good point, but then to make it easier for project stakeholders to be actively involved with requirements modeling and documentation, and to reduce the barriers to entry of stakeholders, one needs to follow the practice like use the simplest tools, using either simple or complex tools like post it notes and flip chart paper to model the requirements and index cards for conceptual modeling. Whenever you bring technology into the requirements modeling effort, such as a drawing tool to create “clean” versions of use case diagrams or a full fledged CASE tool. you make it harder for your project stakeholders to participate because they now need to not only learn the modeling techniques but also the modeling tools. By keeping it simple you will encourage participation and thus increase the chances of effective collaboration.

During the development it is quite common to model storm for several minutes and then code, the common Agile practices such as Test first design (TFD) and refactoring, for several hours and even several days at a time to implement what one has just modeled. This is where the team will spend the majority of its time. Agile teams do the majority of their detailed modeling in the form of executable specifications, often customer tests or development tests. And this will work because your model storming efforts enable you to think through larger, cross-entity issues whereas with TDD you think through very focused issues typically pertinent to a single entity at a time. With refactoring you evolve your design via small steps to ensure that your work remains of high quality.

Agile allows the team to quickly put essentials together and release them into use. This encourages "yes"

or "no" feedback and suggestions. A key advantage is fast failure. If it ain't gonna work dump it or change things for the better. Agile is like Solutions Focused thinking, in going for a little bit that works in the general direction of the end go, verify, reflect, repeat process.