Friendly greeting is of greater importance, we’re told (4)
I believe the answer is:
hiya
'friendly greeting' is the definition.
'hiya' can be an answer for 'greeting' (I've seen this before). I am not certain of the 'friendly' bit.
'of greater importance we're told' is the wordplay.
'of greater importance' becomes 'higher' (I've seen this in another clue).
'we're told' shows a homophone (sound like).
'higher' is a homophone of 'HIYA'.
'is' is the link.
Can you help me to learn more?
(Other definitions for hiya that I've seen before include "Informal 19 across" , "modern form of salve?" , "Hello!" , "Informal greeting" .)