Excellent advice not to squint so much (8)
I believe the answer is:
peerless
'excellent' is the definition.
(I've seen this before)
'advice not to squint so much' is the wordplay.
'advice not' becomes 'les' (I am not sure about this - if you are sure you should believe this answer much more).
'to' means one lot of letters go next to another (I've seen this in other clues).
'squint' becomes 'peer' (I've seen this in another clue).
'much' means to remove the last letter (much but not all of the word).
'so' with its last letter taken away is 's'.
'les' put after 'peer' is 'peerles'.
'peerles'+'s'='PEERLESS'
Can you help me to learn more?
(Other definitions for peerless that I've seen before include "Having no equals" , "Without equal or lacking lords" , "Without equal, nonpareil" , "Excellent" , "Outstanding" .)