If it's someone attractive, I make solid eye contact for 3 seconds before looking away. It tells them that I am interested and if they don't break the eye contact, it means they are interested as well.
When it comes to eye contact, I have problems with men because they scare me. I also hate when someone stares just at me when I'm talking. It's creepy. Like, bitch, stop trying to read my mind, etc.
It depends on the person I'm looking at. If it's someone I'm comfortable with, I can usually hold my gaze. But if it's someone that I don't know, I usually have to look away after a while.
I always heard people who always take off their eyes when they're talking to someone are weak and fake. I admit there are some people I can't but generally I do.