Hi Modes fans (I know you are out there!)

I'm just getting to grips with modes, analysing some modal pieces (currently Vaughan Williams' Oboe Concerto). I can recognise the various modes (I think!) but I'm wondering if there are any rules or common patterns about what changes are likely to occur? (similar to likely keys that a piece will modulate into form a standard major or minor key)

Insights appreciated, thank you...