I keep finding more relevant articles to the earlier post.
Keeping bread crumbs comes from this article entitled, Why You Should Always Keep a Running List of Your Accomplishments. OK, I doubt anybody really does this, but keeping LinkedIn updated might be an approximation. The 'observe your own trends' idea is really interesting. Do you know what you do well (and have done well) and do you know what you enjoy doing? There might be things you've done in the past that were most fulfilling at the time, but you've forgotten about them. Perhaps just keeping a remembrance file of accomplishments and 'fun' projects?
And James Altucher just wrote a post on his blog entitled, Do You Have a Plan B? which I recommend. It is OK to have a plan B and a Plan C, and a Plan D, etc. His posts are rather colorful, but his idea of keeping writing down ideas is a good one. I need to be doing that myself. Thomas Edison famously said, "I have not failed, I have just found 10,000 ways that don't work" which is a similar point. It is fine to do something and then change and do something different. Personally, I think that is the way of the future and there will be less cases of people doing the same things across a lifetime.
Finally, Relevant Magazine has stories regularly on finding your calling including So You Have No Idea What Your Calling Is? which was posted just recently and an earlier story called Your Calling Is Closer Than You Think.
Lots of good ideas.