Jingles start to tell on royal poet (9)
I believe the answer is:
rhymester
'poet' is the definition.
(I know that rhymester is a type of poet)
'jingles start to tell on royal' is the wordplay.
'jingles' becomes 'rhymes' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'start to' suggests taking the first letters.
'on' says to put letters next to each other.
'royal' becomes 'er' (abbreviation for Elizabeth Regina).
The initial letter of 'tell' is 't'.
'rhymes'+'t'+'er'='RHYMESTER'
Can you help me to learn more?
(Other definitions for rhymester that I've seen before include "mediocre poet" , "Writer of short poems" , "Inferior poet" , "Would-be poet" , "Poor poet" .)