Thank you for the replies, and thank you for the links to other relevant threads. I have a few ideas on what Wu Wei might be based upon other ideas that i've heard. One idea is that we each have a blueprint within us that is our 'highest' path / calling / nature etc.
We see this blueprint in the rest of nature. For example, a rose bush has the blueprint of a rose bush within it and can only be a rose bush. Where humans differ is with that we seem to have some free-will. Each of us has our own unique blueprint within us, but we are free to ignore it and live whatever life our circumstances allow us.
How can we know our blueprint? Our passions, interests, talents, inspiration excitement, enthusiasm, interests etc. all signal what our blueprint is. If we follow our passions etc. then - to the degree of commitment - we fulfil our blueprint. Wu Wei (effortless action) is the process of following our passions, interests, enthusiasms etc.
Most of us will have had this experience at various times when we have 'acted' on inspiration or engaged in a passionate activity whereby we become immersed in what it is we are 'doing' and it has been easy, natural, flowing, no effort. For example, sometimes I play guitar and create pieces of music with such ease - no thought, no effort, no action being taken on my behalf, it just happens... it's a happening that occurs through me not an action that occurs because of me.
So, this is how I am coming to understand Wu Wei. The key is to identify my passions (this requires some excavation), to immerse myself into moments of inspiration and let whatever will be unfold, and to attempt to translate this effortlessness into all moments, i.e. connecting the dots of excitement, moving from one inspiration to the next. I haven't experienced it yet, but I suspect it is as self-propogating process, i.e. the more that I engage with what inspires / excites me, then the more inspiration and excitement comes into my life to continue moving forwards.
I'm not sure how well i've explained this, but my thoughts are coming together somewhat and I appreciate the opportunity to discuss it with others.