Student beginning to work in boozer (4)
I believe the answer is:
swot
'student' is the definition.
(I have seen 'diligent student' mean 'swot' so perhaps 'student' could also mean 'swot')
'beginning to work in boozer' is the wordplay.
'beginning to' says to take the initial letters.
'in' is an insertion indicator.
'boozer' becomes 'sot' (I've seen this in other clues).
The first letter of 'work' is 'w'.
'w' going inside 'sot' is 'SWOT'.
(Other definitions for swot that I've seen before include "One studying too much" , "Nerd" , "Student who studies harder than others" , "Study too much - or the student" , "Of student, study hard" .)