When it comes to eye contact you need to remember only 2 techniques. Not many, but you need to make them a part of yourself. Always use them whenever you are on stage!
Scan and stop.
In terms of eyes you never speak to the entire audience, you always speak to only one person. Have a conversation directly with one person, look him or her in the eyes. After you have logically completed one idea, which usually is 10-20 seconds scan an audience and then stop your eyes on another person. Repeat this process again.
Cover the entire room with eye contacts. Randomly pick people who you look at in the front row, in middle of the room, on the left side, on the right side, in the back. When you look at one person you will connect with entire audience. Look one person in the eyes, talk to him or her, scan the audience and look another person in the eye. This is the only way you can look at you audience and there are no other options.
Some people may advise to look at the line of horizon, because it will seem that you look at the entire audience. No! You will look like a person who doesn’t look people in the eyes and is insincere. If you look one person in the eyes you look the entire audience in the eyes. If you look at the entire audience, you don’t look anyone in the eyes.
Stop on Mr. Happy more often
No matter how good you are on stage you will always have people in your audience who like your speech and who negatively perceive your message. Imagine that you speak in front of 200 people who enjoy your speech and there is only one man, who constantly looks at the watch and frowns. Who will you look at, the most often? Yes, you will look at this man and think “Am I saying something wrong? I’ll try to convert the negative man into a supporter by all means.” Do you know what happens next? You lose your energy after looking at the negative man and all 200 people suffer by not hearing your best presentation.
When you scan the audience and pick people for eye contact pick positive people more often. Get energy from them. Don’t concentrate on one negative person that sucks your energy. Share good energy from positive people with the entire audience.