There is no real etiquette in the game i'm afraid.
Expect friendlies to fly straight through you to get you killshot,
count on them to drag a con onto your 6 to save themselves,
always expect them to steal your kill,
a deliberate lack of check 6's to get a merge,
Despite a reasonable "no thanks i'm good" jump in on your good 1v1 anyway,
say thankyou for the requested vehicle supplies only to see troops running past,
probably more, can't think right now