I've been exploring this exact question and have come to some unexpected conclusions. For me, the responses you've gotten so far aren't very helpful primarily because they misunderstand the problem.
I start with the premise that 1) We can identify periods of our lives that felt meaningful/purposeful, etc and 2) Creating a life where we feel that way more often is an attractive goal.
If you don't agree with those premises then the rest of what I'm going to write won't be relevant. My guess is you do, and so do most of the people responding to this thread.
Now the tricky thing is that while we can identify the periods of our lives that felt most meaningful, it's incredibly difficult to define meaning/purpose in the abstract. This is an unfamiliar problem for most of us. It's my experience that most analytically gifted people live their lives by establishing a set of clear goals that we then use as lenses for making day to day decisions.
If my goal is to have a large impact on the world I have enough of a sense for what that looks like that I can make decisions about what to focus on to make it more likely that will happen. The same can be said about spending more time with friends, or working on challenging problems. We can confidently visualize what the world looks like where we are doing those things, and set ourselves to the task of making it a reality. (Goals are actually proxies for feelings we want, but that's a topic for another day).
The confidence (accurate or not) that we can achieve these goals is what gives us the motivation to pursue them. From an adaptive perspective it's clear why this is the case. Pursuing impossible goals leads to wasted time and resources, so you would expect our motivation system to be directly influenced by the likelihood of success.
This presents a challenge for our desire to experience more meaning and purpose. Without the ability to define meaning in the abstract we can't confidently visualize a future where they are present. This makes it extremely difficult to know what to orient towards, and even we can tell ourselves a story that seems plausible, challenging to conjure the motivation to pursue it.
It may be that this is in fact by design. We have all had the experience of returning to activities or modes of being that once felt extremely meaningful, but no longer produce the desired effect. Simply replicating what's been meaningful in the past isn't the best strategy. My belief is that meaning/purpose is a different kind of thing and we need to use a different mechanism than we do to achieve other kinds of goals in order to produce more of it in our lives.
We can't orient towards meaning and purpose in the way we do for professional success, but we can train ourselves to make decisions that lead to more of it.
The first step I recommend people take is to describe the meaningful experiences in their past in as much detail as possible. This has two benefits. First you're training your brain to recognize those states. The more detail you go into and the more experiences you unpack, the more you're conditioning yourself to recognize all the subtleties that made that experience meaningful. Focus on the other feelings that were present during those periods. Did you feel challenged? Supported in a certain way? Were you learning? Playing? In my experience the specific constellation of feelings associated with meaning will differ for each person which is why the prescriptive definitions of meaning don't resonate for most of us.
I think of feelings as highly compressed data formed by our lived experience rather than the ideas we have in our minds. This is the domain of meaning, and in order to orient towards persistently meaningful lives, we need to actively engage with that system.
By training yourself to recognize the feelings associated with your past experiences of meaning, that awareness becomes available to you in your day to day life. You can ask yourself if a particular choice is more or less likely to lead to more meaning, and with enough practice you will feel an answer.
You can think of this a lot like physical skills that you learn. You know how to ride a bike, but you couldn't teach someone else how to do it simply by describing it to them. Your body learns the highly complex series of motions you need to perform in order to stay balanced while peddling, all without you needing any conscious understanding of how it works.
The world is infinitely complex and we can't pay attention to everything in our environment. When you climb onto a bike you automatically attune to the inputs you need to be aware of in order to ride it successfully. Orienting towards meaning requires a similar action. You need to proactively put yourself in a frame of mind that preferences the inputs that will help you make decisions that lead to more meaning.
Once you've trained yourself well enough on your past experiences you can ask yourself if a certain decision is likely to lead to more meaning, and more often than not you'll get a felt answer of yes or no.
Another way to think of this feeling system is as an AI that's simply processing too much data for you to be consciously aware of. It learns the incredibly complex pattern of meaning by training on your past experiences, and is going to be far more effective than your analytical mind in determining what future experiences are likely to produce.
There's some subtlety in how to train yourself most effectively, but this is the general idea, I hope it's helpful!