Smarten up pages around the margin (5)
I believe the answer is:
primp
'smarten' is the definition.
(thesaurus)
'up pages around the margin' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'pages' becomes 'pp'.
'around' means one lot of letters goes inside another.
'the margin' becomes 'mir' (I can't explain this - if you can you should believe this answer much more).
'pp' placed around 'mir' is 'pmirp'.
'pmirp' written backwards gives 'PRIMP'.
Can you help me to learn more?
(Other definitions for primp that I've seen before include "Make minor adjustments to one's appearance" , "Make minor changes to one's appearance" , "brush?" , "Tidy" , "Smarten up" .)