Fine porcelain, for example, trailed by good helper initially during promotional activity (8)
I believe the answer is:
eggshell
'fine porcelain' is the definition.
'eggshell' can be an answer for 'porcelain' (I have seen 'Thin porcelain ' mean 'eggshell' so perhaps 'porcelain' could also mean 'eggshell'). I am not certain of the 'fine' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for eggshell that I've seen before include "that soldiers have to get through" , "destined to be cracked?" , "Thin, translucent china" , "manufactured in layers?" , "Yellow and white container" .)