Most watchful, bravest on manoeuvres (9)
I believe the answer is:
observant
'most watchful' is the definition.
'observant' can be an answer for 'watchful' (I've seen this before). I'm not certain of the 'most' bit.
'bravest on manoeuvres' is the wordplay.
'manoeuvres' indicates anagramming the letters (letters manoeuvred in a new way).
'bravest'+'on'='braveston'
'braveston' is an anagram of 'OBSERVANT'.
Can you help me to learn more?
(Other definitions for observant that I've seen before include "Perceptive" , "Heedful" , "Sharp-eyed" , "with a keen eye" , "(Of music)using conventional keys" .)