I started simple and didn't worry at all about TEOTWAWKI. I just worried about one day. I turned off the electricity, water and gas supplies and imagined all shops were closed, roads were blocked and digital media were unavailable. I figured out what I needed to be comfortable that one day, and what I had on hand to provide light, warmth, cook food, water to drink etc. Even a simple thing like flushing the toilet is something I needed to think about. I then set about obtaining those things.
Then I went to three days. What extra things would I need in place to manage three days with no utilities, no shops etc? I set about putting those things in place -- things like emergency water supplies, firelighting supplies (and skills I had to learn), lighting, natural warmth and cooling, first aid, entertainment and so on. After that I started keeping my car full of fuel at all times and thought about where I could evacuate to if necessary. Then I checked out the lists around of 72 hour emergency packs and made sure I had everything on those lists and created two 72 hour packs -- one for the house, one for the car.
Then I went to three weeks, three months, six months, and so on and set about obtaining the things to not only survive but thrive for those longer periods. This included learning new skills like how to grow food, collect and save seeds, how to preserve food, how to make clothes, clean water, and a host of other skills. And all the time I was enlarging my storage of foods and other basics and learning how to store them. I also got out of debt.
It wasn't until then that I really started to think about the collapse of society and all the other crap that's going on. I still think a global depression with food storages and money becoming worthless is the most likely thing most of us are likely to deal with in the short to medium term and that's my main focus. The biggest worry I have is that the shortage of intelligence, self-reliance, and skills in the general population will make them panic when the SHTF.