The most common and most likely answer to this crossword clue is the 4 plus 2 plus 3 plus 6 plus 4 letter word LOOK ON THE BRIGHT SIDE
I've seen this crossword clue in The Times
L
O
O
K
O
N
T
H
E
B
R
I
G
H
T
S
I
D
E
More clues leading to the result LOOK ON THE BRIGHT SIDE
Buddy explains!

The straight part
We know that "cheer up?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cheer up? = look on the bright side.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.