Reasonable indication of approval about to be announced (3,3)
I believe the answer is:
not bad
'reasonable' is the definition.
(I've seen this before)
'indication of approval about to be announced' is the wordplay.
'indication of approval' becomes 'nod' (I've seen this in another clue).
'about' is an insertion indicator.
'to be announced' becomes 'tba' (this might be a standard abbreviation I've not previously seen).
'nod' placed around 'tba' is 'NOT BAD'.
Can you help me to learn more?
(Other definitions for not bad that I've seen before include "Grudging praise" , "Fairly good, all things considered" , "Negative sort of praise, fairly good" , "Quite good" , "Middling (so good?)" .)