Rules for Xmas crackers interrupted by vino, regularly (6)
I believe the answer is:
axioms
'rules' is the definition.
(I've seen this in another clue)
'xmas crackers interrupted by vino regularly' is the wordplay.
'crackers' indicates an anagram (informal term for mad).
'interrupted by' indicates putting letters inside.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'vino' are 'io'.
'xmas' is an anagram of 'axms'.
'axms' placed around 'io' is 'AXIOMS'.
'for' acts as a link.
(Other definitions for axioms that I've seen before include "The truth of these sayings are self-evident" , "Accepted general truths or principles" , "Maxims" , "precepts" , "Self-evident truths" .)