This is the one most important piece of advice everyone should follow, and it results in a much better life overall (including not being subject to being in echo chambers.
Make it a core value to follow truth. For everything you do, everything you know, and anything that comes your way, ask yourself "to what certainty do I know that this is true, and why?"
For example, you may think that eating a certain food is good for you. Do you know this is true? Do you have a reliable metric that you can validate whether this is true or not? Reading a research paper, that has a percentage of people that felt better isn't it - how do you know that you are not in the smaller percentage group that didn't feel better?
If you adopt this view of the world, its pretty easy to not get stuck in echo chambers. You naturally start to see all your personal biases, realize stuff you don't know, and adjust your thinking and actions accordingly. Obviously it takes practice to do so, and its hard to break out of those patterns, but generally, once you get started on this path, its a self rewarding loop.
A really good test along the same lines is asking yourself or another person about yours/their viewpoint "what would you have to see to change your mind?". You will find that the more intelligent a person is, the more they can answer this, because it indicative of the above thought process.
Meanwhile, for average people, they will often answer "there is nothing you can say to change my mind on something", which to them seems like a virtuous statement, but ironically you can trace this sentiment as the root cause for a number of problems in their life.
Seriously. Offset your online interactions with in person interactions. You'll notice people are much more able to engage with contradictory viewpoints when they are looking another human in the face, rather than using computers to mediate dialog.
The internet is biased towards your interests in a way that the real world isn't. Often the cultural geography of a place is a whole package, you can't just pick your own little bubble like on reddit or HN. Even if you just go grocery shopping or go out to public places and events, you'll run into different kinds of people.
And a lot of this is subconscious.
It's not rational.
If you feel that certain web pages, communities, or apps are not meant for your group or you identify them with another group that you don't want to be associated with, then you will not enter them. You will see a different feed of information and social activity or opinions. That feed will largely subconsciously determine your own framing for the world.
With everything else, I really listen (meaning I'm seeking to understand their view, not trying to formulate a counterargument) to what people outside my social circle say when they're expressing their opinions. I'm not always good at that, but I try my best.
You’ll quickly realize that you don’t really “know”.