Miserly at first, you and I will have good intentions (4,4)
I believe the answer is:
mean well
'have good intentions' is the definition.
(I've seen this before)
'miserly at first you and i will' is the wordplay.
'miserly' becomes 'mean' ('mean' can be a synonym of 'miserly').
'at' is a charade indicator (letters next to each other).
'first' says to put letters next to each other.
'you and i' becomes 'we'.
'will' becomes 'll'.
'mean'+'we'+'ll'='MEAN WELL'
(Other definitions for mean well that I've seen before include "Want to he helpful" , "Having intention to act properly" , "with good intention" , "aim to please" , "Have good intentions but poor performance" .)