I would be curious as to what hints there might be for forming the D chord. For my students it was always a struggle to get the ring finger (2nd string, third fret) close enough to the fret to make a clear note. Coupled with that was the likelihood that ring finger would be touching the first string enough to buzz or deaden the note. Then, to make matters worse, in moving the ring finger into a good position, the other two fingers (index, third string, second fret and middle, first string, second fret) would be dragged toward the fret to a point where their respective notes buzzed. What a nightmare! My only advice was to fiddle around with their thumb placement until they got the optimal position for the other fingers and then practice, practice, practice.