Here's the big picture of how I go about this.

1 - What's the total processing time?

2 - What's the query processing time?

From there you know where it hurts (SSAS, or SSRS). If it's pretty much 50% / 50%, then make sure the query is running as fast as possible.

3 - Can you remove groupings?, can you remove calculated columns and do it in the query?, do you have a lot of conditional formating?, do you have .net code that runs on the details?

That list goes on for quite a while...