Small encouragement to take my top plotter (7)
I believe the answer is:
schemer
'plotter' is the definition.
(synonyms)
'small encouragement to take my top' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'encouragement' becomes 'cheer' (I've seen this before).
'to take' means one lot of letters goes inside another (inserted letters are taken in).
'top' indicates taking the first letters (in a down clue, the first letter is top).
The initial letter of 'my' is 'm'.
'cheer' placed around 'm' is 'chemer'.
's'+'chemer'='SCHEMER'
(Other definitions for schemer that I've seen before include "Plotter, conspirator" , "He plots and plans" , "Plotter and planner" , "One making devious plans" , "one inventing plots" .)