Here are some ways you can practice good eye contact:
1) Lock eyes with yourself in a mirror
Practice this everyday, until you can hold this for a few it minutes without changing your expression.
2) Practice on people you pass on the street
If you're really bad with automatically darting your eyes when someone looks at you, you can first start out with mirrored or dark sunglasses. This way, when you're tempted to automatically look away, you're always reminded that they can't see your eyes.
Observe how other people manage their own eye contact and take mental notes of what it communicates. This way you'll start to see and really understand what type of eye movements show nervousness, and what type of eye contact shows strength or confidence.
Without any sunglasses, try to make eye contact with every woman you see on the street. Hold it for as long as you can. Give them a nod and a smile if that helps. You should practice this until you get to the point where you can lock looks with them until they break it first. In most cases, she'll look down from your stare, which is a sign of submission. (Not always a sign of interest, mind you, but it is a good sign of your dominance.) Learn to enjoy it when a woman looks away in embarrassment.
3) Practice on Store Clerks, Cafe Baristas, and Bar Staff
If you are having trouble staring directly in someone's eyes, practice on baristas, store clerks, and bartenders. If you're ordering something, look them straight in the eye with a smile and tell them what you want. This is a good way to practice because they won't be weirded out by it – it will actually make their day. Most people don't look at them in the eye at all, and they feel like non-existent beings that nobody ever acknowledges. Look them in the eye, smile, and say thank you. Usually when I do this the barista or bartender busts into a smile. It's so rare for them that they sometimes even give me the drink on the house. Try it!
Tying it all together
Something fun you can do at a bar with your eyes is to look above a girl at the ceiling like there is something hanging over her, or look past her over her shoulder. If she sees you looking, she'll first look at what you're staring at, and then she'll turn back to you. Once she turns back to you and stares at you, this is when you bring your eyes back to her. Now she's the one who got caught checking you out first. You can then go up to her, introduce yourself, and bust her for checking you out. She'll most likely laugh. Take it from there.
When you are trying to attract someone and show them you are interested you can talk and listen with your eyes. When a person you like is speaking use the whole face as your focal point. Look at their eyes, listen to what they are saying, smile in the appropriate places, raise your eyebrows in the appropriate places.
If you feel you are staring at them move to their other features such as their lips, their cheeks, their nose and then back to their eyes. Smiling when listening to someone is a great way to show you are interested in them, obviously don't smile when they have just told you their pet died last night. You have to listen with your ears as well as listening with your eyes (yes I did mean listening with your eyes, you listen to someone's body language with your eyes).
You don't want to stand there like a fool and make your goal to just focus on staring into the girl's eyes – remember to listen to her if she's speaking. Look for cues as well when you're talking to her.
The basic components of eye behavior are easy to master, once you know how they work. It is important not to make eye contact look deliberate or controlled. The goal is always to use your eyes in a relaxed way so that you never make others feel uncomfortable.