When it comes to Body Language/Nonverbal Communication, people often ask, "Does eye contact mean I have to look the other person directly in the eye all the time?" (or some variation thereof). The short answer to this is definitely "NO". Here's the long answer: If you look directly into one eye - or switch back and forth between eyes, this is too intense and is almost always is interpreted (depending on the other signals and context) as either predatory, anger, sexual attraction or deception (lie detection). But take heed - liars may also go the complete opposite route and totally avoid eye contact though.
So if you're feeling none of the above emotions and you're participating in healthy conversation, "eye contact" should effectively mean looking semi-randomly around the area outlined above on the lovely Keira Knightley's face. I say "semi-randomly, because you gaze should briefly fixate on one of their eyes and then very quickly (and very briefly) fixate on some other portion of their face within this ellipse - and then return to the same or opposite eye. All this time you never want to fixate on one area too long or too intently. We all behave this naturally when we have good rapport during natural conversation.
Having defined "eye contact" as sometimes not looking at the eyes, but close to them - may seem contradictory, but this is what we do during healthy conversation. We should have eye contact (as defined above) between 40 and 70 percent of the time during conversation - and closer to 70 percent if we want to gain or maintain superior rapport.