An important aspect of successful deliberate practice is access to immediate informative feedback and knowledge regarding the results of your performance. Adding this simple, but challenging exercise to your Origin-Destination (O-D) line exercises can offer important insight into what line directions/orientation need the most work:
After a sheet or two of O-D exercises, perform a diagnostic wheel to see where you are weak. Lines that waver or drift off course signal directions/orientations that need attention during practice (obviously the drawing wheel is not to be rotated.) When finished, proceed with another sheet or two of the O-D exercises, focusing on the weak line directions/orientations in an effort to garner improvement. When you are finished, perform another diagnostic wheel to again assess development. Repeat as necessary until you can confidently make consistent lines around the entire wheel.
