Currently I'm only at rank 16. Best rank I have had was 12 or something like that so nothing impressive.
I don't know if its true but it seems I'm having insanely bad luck in this game so that's why I keep staying at bad ranks. Last time opponent had no cards left and drawed deathwing and won the game by 1 health even thought it seemed he had like 0 chance to win. :/
I haven't really tried, I think the best I got was like rank 7 a year ago. I would just log in, do daily quests and arena really. However now that getting a high rank rewards you, I'm going to aim for rank 5 (best reward).