One of the secrets to getting a really professional finishing job is good sanding. But sometimes, getting down into those detailed areas can be a bit tricky. Here's a suggestion to make the task easier.
Cut off a piece of jute twine a couple of feet long, and wrap it right into the groove that you are trying to sand.
Cross the twine over, and pull it back and forth. There's just enough abrasive on this twine to really get in there and do a great sanding job.