I've found that it's mostly about being well connected through social media and attending other events/meetups. You'll still miss things, but even sites such as Lanyrd won't list everything.
As somebody who is getting more and more involved in organising local tech events in my area I'm interested in this myself. I'm running a Google calendar and Twitter account to highlight the best local events (mostly non-tech based) but feel I could be doing better.
