I don’t claim to be an expert, however with 25 years of Toastmasters speaking opportunities, I am experienced and feel comfortable in providing an answer.
The simplest and perhaps most precise answer to the question of where should I look… would be to look at the audience.
So what does that mean? I don’t like giving speeches. However, I do like having conversations with groups of people. I tend to think of a speech as a one-way data dump. You are often pressured to get your message out at the expense of your audience.
When you think of having a conversation with your audience, as I am suggesting, you are open to interaction with them. This interaction can be elicited by asking rhetorical or even direct questions to them.
It is easier to make eye contact when conversing versus preaching. Many speeches are preachy. That one -way data dump I referred to earlier.
A technique I had heard that helps reduce your reluctance to maintain eye contact with your audience is to greet people at the entrance, when they come in to sit down. That way, when you are speaking to them in your presentation, you are speaking to the as friends, not strangers. I have found it helpful and I can tend to be on the shy side. One caveat is that you want to protect your voice when you are greeting people so it will serve you well when you do speak.
The beauty of making eye contact with your audience is that many of your audience members will feel that you are speaking to them directly. Connecting with every audience member should be your objective. Otherwise, why bother speaking at all?
As answered on Quora.com