Gain new accommodation before crusade (8)
I believe the answer is:
campaign
'crusade' is the definition.
(I know that crusade is a more specific form of the action campaign)
'gain new accommodation before' is the wordplay.
'new' indicates an anagram.
'accommodation' becomes 'camp' (I am not sure about this - if you are sure you should believe this answer much more).
'before' is a charade indicator (letters next to each other).
'gain' anagrammed gives 'aign'.
'aign' put after 'camp' is 'CAMPAIGN'.
Can you help me to learn more?
(Other definitions for campaign that I've seen before include "Series of actions toward a particular end" , "Series of battles (8)" , "Promotional operation, perhaps political" , "(E.g. military, political) project" , "offensive" .)