We are having a hard time meeting Sprint comits, one reason I suspect is that we are not doing a good job estimating and one of the causes of this is that we don't do a good job decomposing the story down to a sufficient level of granularity to fit within the sprint.
I see a lot of comments on Agile that it is critical to have granular stories that are small enough to fit in the sprint, but I have not found any recommendations or best practices for HOW to decompose a story to the correct level of Sub-Task granularity.
Does anyone have good practices or heuristics as to what is the "right" level of granularity?