If your knife is sharp and you’re comfortable with it - my tip for an even cut would be to trim one end so that it is flat, (assuming right handed otherwise reverse this), place your left palm flat on the cut end (rest of roast pointing to right) with fingers spread, now cut steak with right hand.
I don’t know the neurological backbone of this but your brain somehow knows in space where your left hand is and tries to keep what your right hand is doing parallel.
A similar trick can be used when cutting long strips of say dough with a pizza wheel. Put your finger on the opposite end of the dough and roll towards your finger - for some reason it helps keep you on track better than eyeing it. (Of course a long ruler is better but it helps a lot).
