Becoming crafty keeping tabs on Mike (6)
I believe the answer is:
seemly
'becoming' is the definition.
(I know that becoming can be written as seemly)
'crafty keeping tabs on mike' is the wordplay.
'crafty' becomes 'sly' (sly can mean crafty or cunning).
'keeping' indicates putting letters inside (some letters kept inside).
'tabs' becomes 'ee' (two E's - E can mean an Ecstasy tablet).
'on' is a charade indicator (letters next to each other).
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'ee'+'m'='eem'
'sly' going around 'eem' is 'SEEMLY'.
(Other definitions for seemly that I've seen before include "Conforming to good taste" , "Decorous or proper" , "Appropriate" , "Decent - handsome" , "Part of the foot" .)