Fancied a little drink and sit down at first (8)
I believe the answer is:
supposed
'fancied' is the definition.
(fancy can mean to suppose or imagine)
'a little drink and sit down at first' is the wordplay.
'a little drink' becomes 'sup' (sup can mean a small drink).
'and' means one lot of letters go next to another.
'sit' becomes 'pose' (as in sitting for a painter).
'at first' suggests taking the first letters.
The first letter of 'down' is 'd'.
'sup'+'pose'+'d'='SUPPOSED'
(Other definitions for supposed that I've seen before include "Assumed without proof" , "Generally believed" , "As expected" , "Imagined; assumed" , "Reckoned, took to be the case" .)