Given, you have to talk to them too, usually. This, however, is one of the easiest secrets to learn in seduction and also one of the most powerful. The principle applies to both sexes.
Spend about 20 minutes a day or more practicing this in front of a mirror. The look you want in your eyes could best be described as "intense". Think lustful thoughts and imagine you are looking at someone who drives you wild. Simply.. try to be passionate.
Once energy is surging through your body, you want to transmit this only through your eyes. Your face should remain deadpan. Use visualization techniques if it helps. As you get better at this, you'll be able to turn it on. You'll be able to make your eyes go from "dead" to "very much alive" in a few seconds. This skill of making your eyes transform has a powerful effect!
Combine purposefully banal talk with intense eye contact. Because you're sending out mixed signals and being indirect, the other person will often tune out from what you're saying and lose themselves in your gaze. It also doesn't give them a chance to analyze what's going on, they'll pick up on your flirtation subconsciously.
Realize that this won't suffice on its own; it is merely a good ingredient of complete seduction. You still have to go out and meet people. However, your new found expressiveness will work very well in nightclubs, where non-verbal communication is the order of the day.
You can use this all the time, but you don't want to go around "turning your eyes on" at people. You should just have an alert, attentive look. Holding eye contact for a second longer than normal can say everything.
The power of this can't be overestimated. You'll find people becoming drawn to you. You literally gain power, and all because you simply look like you already have it. It is essential for charisma.
Try closing your lower eyelids a little, like you're squinting, but keep your upper eyelids fully open. You'll find you can go for a long time without blinking.
The triangle gaze: once in awhile when you have eye contact with your target, glace down at their lips, hold the gaze for a moment then back to one eye and over to the next. This is extremely effective.
It's very important to keep your gaze ambiguous. You don't want to look angry or scared, often you might not even want to look sexually interested because if your expression can be read that easily, then the illusion is broken.
Just go for intensity and warmth, as if you can read the other person's thoughts, but they have no way of reading yours.
Don't look insane. You can take this thing too far. Look alert but be physically relaxed.