Try focusing on the line between the colour and the white of the eyes. And always focus on the near-side eye to optimise depth of field. If you can, make sure the near-side eye is also the dominate eye i.e. the larger one
|Julia at Abbey Farm. Nikon D700 85mm Nikkor 1/320s @ f2.8 yellow filter|
That's just for starters.
And don't click until you get a great 'eye-meet'. A flirty, soulful, in-your-face, genuine eye-meet. If I could put one new feature on a camera it would be a shutter that wouldn't fire unless you've got an eye-meet.
Create the intensity, the emotion, the feel. You need to be so confident with your camera that you hardly ever look at it.