It's good that you're practicing a variety of eye shapes. I think one thing you might work on is that the black linework for the eyes is very rough and a bit jagged but the eyes themselves with the pupils and the irises are very smooth and blended. I'd try sticking with either one style or the other instead of having smooth blending right next to sharp lines. I think I'm liking the bottom left eye the most, personally.
Well I think what they mean is that it's far easier to see expression when there's two eyes together instead of just one. One eye working on its own doesn't have half the expressive ability as two eyes together. At least that's what I think they meant.
drawn in 8 min