Dont forget the poision resists too.
generally, i usually start to planeshift, BM, and EU right before I accept the duel, then I recommend opening with Earthquake (knockback), stun him, stick all your dots on him and watch him die

Communion can be handy because the Earth pet knocks back etc.
Also dont forget you can stoneskin etc. Can save your butt if he manages to stun you at the beginning / if you get reisisted.
(My brother is a necro, needless to say, I duel him once in a bit

)