I found two things really helped to create ah-hah moments for me in getting the not-self teachings:
Inspecting mental objects for impermanence, suffering, and yes, not-self
Reading the latest in neurobiology for lay people, as much research and study is going into how the brain creates not one, but two illusory selves and why
I understand Candol's confusion in sitting there asking is this me, is that me, etc. Now when I do that, I totally get it. But in the beginning this voice inside would scream, yes *I'm* right here, stupid. Of course there is a me! Indeed there is a me, not just one, but two, three, four, and now I see literally hundreds of me arises in a single day! But here is what I discovered. . . .
In focusing on impermanence of mental objects: thoughts, judgements, emotions, etc., I saw the fleeting nature of my mind. Thoughts not only come and go, I have no control over what kind of thoughts arise. I do seem to have some control over which I choose to follow. More importantly, I started discovering attachments to certain thoughts, identification with certain thoughts as me. But I often change my mind, opinions, and thoughts zip in and out continuously. So why identify with them? Why allow these shifting winds to define who I am? Suddenly it seemed absurd to do so.
In being mindful of my thinking processes, I realized I could let go of attachments to my ideas. I didn't have to be right. In fact, in watching closely, I discovered I'm sometimes wrong! I felt myself opening more other others in this process. The me I'd been clinging to, trying to define through my mental ideas was shrinking, become less important. I realized, ah, this is what Buddha meant by we are not our thoughts. There isn't a static, permanent self in thoughts. They are simply thoughts we can allow to pass through.
I also saw how many of my mental processes caused my own suffering, by my being attached to my own ideas, by ego bubble bursting when I'd realize I was wrong about something, and the way my thoughts would feed anger, sadness, judgements. Now, because I'm just seeing thoughts as fleeting things passing through, they have lost the power to create so much suffering for me.
The neurobiology books helped hugely in explaining how interconnected networks create an illusory sense of self through processes. The self is not a thing, it's a multitude of processes. The brain doesn't have a central processor like a computer, a driver, but instead creates this illusory, or feeling of self, so that you'll care enough to eat and protect yourself. The other self it creates, that seems to be more a human mental process, is the self that observes itself, or what we experience. This is vital to learning.
When I read about this in terms of biology and evolution, it made perfect sense physically, and it helped make sense of what the Buddha taught and what I was observing in my meditation and mindfulness throughout the day.
The problem is not that we have a sense of self. We need that for survival, for learning, for creativity. The problem is when we "identify" through these impermanent processes. I had this thought, therefore it is true, and anyone who challenges me is going to piss me off! THAT is a problem. Whereas if you are mindful of your mental processes and see how fleeing there are, you can be flexible and dynamic, willing to let them go if they are determined to build some story that fuels anger, or let them go when you discover they're just wrong.
That was probably way longer an explanation than anyone wants, but that has been my discovery and understanding of not-self. It's learning not to identify with and build ego around our thoughts, our bodies, and create this sensitive, destructive illusory self. I suspect this is just the surface of the the not-self teaching, but I find it all fascinating!
BTW, this was an area that I was determined to prove the Buddha wrong, wrong, wrong because I felt sure my intellect was ME! Thankfully I've discovered that just isn't so! I feel more dynamic for letting go of the ideas and attachments I had about myself.