1. attuned to the requirements of something, performing smoothly and efficiently
I struggled at first, but once I got in the groove it was easy
To be 'in the groove' means to perform well, be up to date or enjoy yourself. You can 'get into a groove' with work, meaning to perform to a high standard. To 'get in the groove' is something someone might say in reference to enjoying music or dancing. This is a very colloquial term used mostly in informal contexts.