Order it up when you have a meal on the ship (8)
I believe the answer is:
'order' is the definition.
(I know that tidiness is a type of order)
'have a meal on the ship' is the wordplay.
'have a meal' becomes 'dine' (I've seen this before).
'on' indicates putting letters inside.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'ship' becomes 'iss' (I can't explain this - if you can you should believe this answer much more).
'dine' put inside 'tiss' is 'TIDINESS'.
'it up when you' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tidiness that I've seen before include "Insisted on neatness." , "Quality of neatness and orderliness" , "sense of order" , "good order" , "Orderly quality" .)