When someone is talking to me, I look directly into their eyes.
What's strange is I didn't even realize I did that until I made a comment about a guy having a lazy eye and my mom had no idea what I was talking about, even though she talked to him longer than I did.
When I'm talking to someone else, it's mostly the same thing. I almost always start and end a sentence looking into the person's eyes, but I don't always hold eye contact throughout, especially if I'm not interested in the conversation.
If I'm explaining something more complicated, I usually end up looking down or away as I try to figure out the best way to make sense, but I'm rarely really looking at something when I do that. It's just the normal 'Staring down while thinking about something' look.
And yes, I make eye contact with strangers. Seems rude not too.