... in an office environment or while talking to friends ...
I think you have 2 very different settings and backgrounds here. I never had a problem with family, friends and acquaintances, but I had to train and train (and repeat) again when I had to talk to people in an office or giving a presentation. That's why I'll focus on the professional part. And when you succeed in one, most of the time, you can't miss the other one anyway...
First, it's important to know / learn about the importance of eye contact during a presentation and learn some tips for making eye contact. You can also read about how to overcome eye contact anxiety. (I give very few links, as there are so many you can easily find, some being very useful, some much less, you need to sort this out...).
My only tip, the one I practiced, was to move my eyes following the rythm of the sentences. For instance: when you read for yourself, in your head, you may not "act", and just keep a neutral tone. No matter what you read, the words will do the job. But when you "read" for someone else, you want the words to be "real", and you want the tone that you use to convey the idea behind the words: frightning? loving? joy? pain? sadness? Try to do the same with your speeches to colleagues. Make ideas come to life using the appropriate tone. Slightly emphasize what needs to be, use a quick 1s pause after a punchline or an important fact. Let people catch the idea.
So, when I had to talk to teammates, I would make sure I evenly split the time of eye contact. One idea or sentence to each one of them, more or less. The sentence being directly said to the person, with eye contact. It's like reading a book to children. In your case, talking to adults, you sure don't need to emphasize. And make sure you don't, as it may be seen as patronizing.
If you have people sitting at a table, in front of you, with a 180° angle point of view, split this big area. 3 or 4 smaller areas, filled with 2 or 3 people. Then, talk to these 2 or 3 at the same time, then, move to another area and repeat. This way, people feel like they are important without being singled out. When on a stage (watch videos of great teachers or tycoons giving a presentation and see how they move, learn their body language), you should move from left to right, and back, with small stops. When you can't walk or move, do the same with your eyes and look at them; just like if they were taking turns, one on one.
Practice, and practice again. Keep in mind what you have to say, the idea you want to convey to these people, and "read" it to them. Tell them the story you wrote. Once I realized I was able to do that, I was much less nervous, and much more efficient.