Almost imagine how you'll be after the successful dieting (4)
I believe the answer is:
thin
'you'll be after the successful dieting' is the definition.
I can't tell whether this definition defines the answer.
'almost imagine' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'imagine' becomes 'think' (synonyms).
'think' with its last letter removed is 'THIN'.
'how' acts as a link.
Can you help me to learn more?
(Other definitions for thin that I've seen before include "Lean; narrow" , "With little thickness" , "Carrying little fat" , "Lean; make (plants) less crowded" , "as 7 [LOAF] may be sliced" .)