See something worthwhile in blackguard (5)
I believe the answer is:
louse
'worthwhile in blackguard' is the definition.
'louse' can be an answer for 'blackguard' (I've seen this in another clue). I'm not certain of the 'worthwhile in' bit.
'see something' is the wordplay.
'see' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'something' becomes 'use' (I can't explain this - if you can you should give a lot more credence to this answer).
'lo'+'use'='LOUSE'
Can you help me to learn more?
(Other definitions for louse that I've seen before include "Parasite; nasty person" , "Bloodsucking parasitic insect" , "Common parasite on animals" , "Insect -- nasty character, undeserving of respect" , "From cad" .)