Unhelpful instruction for conserving something? (7)
I believe the answer is:
useless
'unhelpful' is the definition.
(similar in meaning)
I can't explain the rest of the clue.
(Other definitions for useless that I've seen before include "Vain - unavailing" , "Unemployable" , "to no avail" , "Not worth a jot" , "Vain, impractical" .)