For a starting point, you need to understand something that I mentioned in previous posts. When SHTF occurs, the situation is fluid – it can change quickly, and you need to recognize those changes so you can react in time, and in the proper way.
The real danger is other people
I like to say that when the SHTF most probably your enemy is not going to be some foreign invaders, UN troops, or people that are very different than you.
It's very possible your enemy will be the people that today live around you.
What will make them your enemy?
But always the main reason will be the lack of resources, and it is something I wrote about a lot in my book. That makes every person your possible enemy.