Demon dodge and then hitting something knocks the counter up quickly, as does doing the Y,Y, pause, Y move with Arbiter. Also found the holding Y move with Aquila and the trillion stabs move (towards, towards Y then hammer Y with the normal sword) is an easy way to shoot up one rank.
Any tips for getting more style points, I'm going for the SSS on nephilim achievement but can only ever get around S/SS for style as there are far less enemies
Abuse Devil Trigger as well to kick the score up as you'll earn loads of it.
Managed to get SSS on levels 2 to 7 last night in one go using those tricks.