You're on the right track.  Be an active and contributing member in your detachment.  Do well in classes.  Those GPA and Commander's Review are the largest items in the order of merit calculations (which determines who gets to pick their jobs first).  So, to have the best chance at getting a UPT slot, you want to be very high on the order of merit.  That way, you will get to choose before the slots are taken by other qualified people.