I'm sure many of you know that Ian Baker-Finch has become something of a putting and short game guru among PGA and LPGA players. (So Yeon Ryu is one of his students who immediately comes to mind.) I found this short video he did for Odyssey Golf that details one of his putting drills, in case you'd like to see what he teaches.
What I like about this drill is his emphasis on touch and feel, on getting the speed of your putts right. While you want to get your putts on line, more putts miss because they're hit too hard (or too soft) than are missed with a poor line. If your speed is wrong, the right line won't necessarily help you!
Ian's approach is a bit more mechanical than I would teach, but there are so many different teachers simply because not everybody learns the same way -- and of course, you don't have to be mechanical when you practice if you don't want to be. If you're looking for a new putting drill to try, I think this is a very good one. Any time you avoid just hitting the same putt over and over, that's a good thing.