I am playing in low ranks, where people spend 2 mana to play a 2 damage curse, so I can’t really give advices 
but I’ll try.
I start by giving some curses to the opponent (let’s say 2).
After that, I try to give more than one curse at the time, or give curses while building a board, so they have to choose if to take damage from curses or from the board.
I use Azshara to get the “1 mana spell copy”, and if possible I use it with tamsin, so with only 1 curse spell I can give 4 curses to the opponent.
I almost never used the 6 mana spell: it doesn’t synergize with tamsin and it isn’t good if I have a board.
Gigafin is the only real board clear in the deck, so if possible I copy it with zola if I am against mech paladin, for example.
Against quest hunter I still have to figure out what to do maybe concede turn 1 is the best play?