Consider old folio trailing poor Yorick's finale (5,2)

'consider' is the definition.
(thesaurus)

'old folio trailing poor yorick's finale' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'folio' becomes 'f' (abbreviation listed in Chambers).
'trailing' is a charade indicator (letters next to each other).
'poor' becomes 'thin' (I've seen this in other clues**).
'finale' suggests the final letters.
The last letter of 'yorick' is 'k'.
'o'+'f'='of'
'thin'+'k'='think'
'of' after 'think' is 'THINK OF'.