Go on about single doctor first (5)
I believe the answer is:
drone
'go' is the definition.
(I know that drone is a kind of go)
'about single doctor first' is the wordplay.
'about single' becomes 'one' (a single thing - only one. I am not sure about the 'about' bit.).
'doctor' becomes 'dr' (abbreviation).
'first' is a charade indicator (letters next to each other).
'one' put after 'dr' is 'DRONE'.
'on' acts as a link.
Can you help me to learn more?
(Other definitions for drone that I've seen before include "Continuous humming sound" , "He buzzes, but not with energy!" , "Low hum; parasite" , "he gives us a buzz" , "Monotonous low sound" .)