have (something) down to a T
To do something well or efficiently, typically due to one's experience at it. I'm a working mom of three, so I've got lunch-making down to a T—I put out all the pieces of bread, add jelly to each one, and then do the same with peanut butter.
have something down to a T
Fig. to have something mastered. I can do it. I have it down to a T.