When the ball is on an uphill or above your feet lie all you have to do is make some adjustments to your set up and stance
What really differentiates players is their short game, and juniors should take a tip from the pros and spend at least half their practice time on the short game
For most arc putters the conventional putting grip is very much like a regular golf grip but with the thumbs pointing straight down, allowing your arms to be in a more normal golf position