Vivid impressions at first on new future, for example (7)
I believe the answer is:
intense
'vivid' is the definition.
('intense' can be a synonym of 'vivid')
'impressions at first on new future for example' is the wordplay.
'at first' indicates taking the first letters.
'on' means one lot of letters go next to another.
'new' becomes 'n'.
'future for example' becomes 'tense' (future is a kind of tense**).
The first letter of 'impressions' is 'i'.
'i'+'n'+'tense'='INTENSE'
(Other definitions for intense that I've seen before include "Excited" , "Extreme - strong" , "'Ardent, forceful (7)'" , "Deeply felt - extreme" , "Vived, extreme, acute" .)