Used to work for Monarch pre 2001 and Long haul does vary no real system for alocation of trips. The girl i lived with was also crew on same fleet 757, A300 and A330 as me used to get some fab trips.
I used to get 3 weeks short haul ..... Palma, Malaga, Rhodes there and back or taxi to Man. Then one 24 hour layover in MBJ at the end of the month. While her flights used to look like something more from BA staff rosta, ie 14 day trip to Bahrain with postioning flight out and back, five day trip.... Dom Republic then position to Florida and crew back to UK. It all seemed to come down to where your name was on the computer at crewing.