It helps to remember conmen I’m messing around (8)
I believe the answer is:
mnemonic
'it helps to remember' is the definition.
(a mnemonic helps you remember something)
'conmen i'm messing around' is the wordplay.
'messing around' indicates anagramming the letters.
'conmen'+'im'='conmenim'
'conmenim' anagrammed gives 'MNEMONIC'.
(Other definitions for mnemonic that I've seen before include "Verse or other aid to help one remember facts" , "It reminds us" , "Something by which to remember" , "Letters aiding memory" , "Phrase devised to assist memory" .)