Goes slowly, like doctors out to get you fit anew (6)
I believe the answer is:
drifts
'goes slowly like doctors' is the definition.
'drifts' can be an answer for 'goes' (drifting is a kind of going). I'm unsure of the 'slowly like doctors' bit.
'out to get you fit anew' is the wordplay.
'out' is an insertion indicator.
'to get you' becomes 'drs' (I can't justify this - if you can you should believe this answer much more).
'anew' is an anagram indicator.
'fit' with letters rearranged gives 'ift'.
'drs' placed around 'ift' is 'DRIFTS'.
Can you help me to learn more?
(Other definitions for drifts that I've seen before include "Floats along aimlessly" , "Wanders or floats aimlessly" , "proceeds without purpose" , "Wanders around" , "Moves slowly, carried by a current of air or water" .)