I like to think of the Three Characteristics as three different ways to describe one truth, the truth of the way things are. A good analogy is the way light goes through a prism. It manifest as different colors, but, it is only one light. The truth of the way things are manifests in Anicca, Dukkha, and Anatta, but it is only one truth. Each characteristic is composed of the other two.
The main reason why conditioned phenomena do not have a solid, lasting self is because of the fact that everything is interrelated and changing. Things do not last long enough for them to be considered a “solid thing,” and so we can see the characteristic of Change embedded and giving rise to Not-Self.
Similarly, Dukkha presents as exquisite unstableness and vulnerability, and gives rise to not-self, especially when looking at the phenomena we call “myself.” If the self was a solid separate thing, we would be able to control it and all mental and physical manifestations of it. But, of course, we are not in ultimate control of our bodies and the contents of our mind. They are unstable and we are vulnerable to their fluctuating nature. This shows that what we call ourselves is Anatta, Not-Self. We can see the instability and vulnerability of the characteristic of Dukkha embedded and giving rise to Not-Self.
We talk about the characteristics as separate things, but in a moment of seeing any one of the Three Characteristics, the other two are simultaneously seen. The truth of the way things are is simply known.
Whenever you notice one of the Three Characteristics, look and see if you can notice one or both of the other two being present. For example, you notice the characteristic of change as the weather gets colder. You might look and see that the change is unsatisfactory to you if you don’t like the cold. You can see Dukkha present in the form of getting what you don’t want.