Having more firepower than you opponent will basically guarantee a win.
Make sure you use the minion's abilities, don't waste then unless really necessary.
And always look ahead, just dont go ''omg legendary, mind control win kk''. Your opponent could aswell mind control it back or just kill it or something...my point is, always look 2-3 moves ahead.
Anyways, I am not a pro or something, just basic stuff that should get you to rank 14 with this deck (give or take a few tweaks).
If you need more than that, then yea, you will need better cards.