The most common and most likely answer to this crossword clue is the 5 letter word PRIMP
I've seen this crossword clue in Financial Times
P
R
I
M
P
More clues leading to the result PRIMP
- Groom's proper place at the front
- Dress up right, with solicitor around
- Smarten up pages around the margin
- Dress up like a proper prince
- Groom runs into bloke with girl
- Pander to house manager finally and smarten up
- Groom, stiffly formal before start of proceedings
- Select short page for groom
- Groom being formal with page
- Get smart advertising demon
Buddy explains!

The straight part
We know that "smarten up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case smarten up = primp.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRIMP mean?
PRIMP verb- To spend time improving one's appearance, often in front of a mirror.
- To dress in an affected manner.