a SSRS 2008 problem:How to increase the response time

I have created a rep开发者_开发问答ort using ssrs 2008.i have used mutiple times of grouping of data.Problem is arise when i preview the report it takes a lot of time ,sometimes more than 40 minutes. how can i resolve it.

See if you can cache the dataset, Microsoft recommends to cache the dataset when the time taken is more then what is expected.

Also read the link http://www.simple-talk.com/sql/performance/a-performance-troubleshooting-methodology-for-sql-server/ which provides the basis for troubleshooting the Query at the database level.