- Having an extensive and varied knowledge as it relates to where you are. It's an infinitely long list to 'know everything' but to give you an idea of what you should learn consider these examples. Just before the devastating tsunami ten years ago in Thailand, the people who were able to escape and run for the hills were the people who knew what the signs of an eminent tsunami were (rapid sea level change not related to the tide, huge waves, etc). Everyone else was quite oblivious until the deadly waves started crashing on the beach. In another example, you can tell city folks because they head for the mountains on a very windy days (trees are more likely to fall on you then) or run from wild animals like bears (you will look like prey to the bear and they will chase you). Drilling down, locals know the risks of certain parts of town and are #1 more likely to avoid dangerous places and thus problems, or #2 know the area well enough, and be known well enough by the local gangs, to know where they can and can't go without problem (although the risk of being an innocent bystander during a drive by increases exponentially so most logical people will avoid such places all together). And the camper who runs out of TP and uses leaves will either #1 know what poison ivy/poison oak looks like, or #2 learn quickly enough. All knowledge is good knowledge but the more you know the more likely you are to be able to put your knowledge to good use during a disaster.
- Paying attention to what is happening in your surroundings. Some people are simply oblivious most of the time which can make them easy victims for crime (like pick pockets or rapists) or can get them injured or killed (I've lost track of how many videos I've seen where people were so busy looking at their cell phones that they walked into fountains, onto railroad tracks, into traffic, etc). Don't be that person. Where ever you go you need to do a quick scan of your area and see what's going on. Usually everything will look "normal" but if you see something out of the ordinary (like a pressure cooker sitting on the sidewalk in a busy city) you should probably take another look (not too closely in the case of the aforementioned incident). Things you should consider: the weather, the day of the week and time, the general political climate, the recent news of the area, the type and age of the building, what the signage says, what, if anything, looks like it doesn't belong, etc.
- Paying attention to people. The 'wild card' in most situations is people. An empty building isn't going to "do anything" unless there is an earthquake or something. A building full of people is a whole different animal. Generally people will act in a predictable manner (actually this is usually only common in semi-rural areas with a close-knit, homogeneous, upper social-economic population), but in more and more situations these days, people can be hard to read. The mentally ill, racially divisive areas, people on drugs, a high population of young men, areas that can inspire anger or violence (like bars and nightclubs), high stress situations, etc. can all lead to unexpected but not unpredictable violent outbursts. While you always need to be on alert when you are around people, the more potential there is for people to have problems, the more alert you need to be to their expression, their tone of voice, the words their use, how they are carrying themselves, if they have any sort of weapon, etc. You want to observe as much as possible in order to be able to formulate a plan of action if needed.
- Making plans for "what if". The last task, when it comes to being situationally aware, is to always have a plan B, C, and D. Plan A might be to hang out at a local bar with your buddies. Plan B would be how to exit the building in a hurry (do you know where all the exits are and who/what is between you and the exits?). Plan C would be how you could protect yourself in the event of an unruly customer or a fight (run, fight, or hide and the usual options). Plan D would be a previously practiced team effort by you and your buddies to come out safely in the event of a disaster (everything from an earthquake to a major brawl).
Being situationally aware requires practice (you should practice observing your environment all the time). By becoming more observant, blending what you observe with your general knowledge, and formulating "what if" plans, you will be way more aware, and way more likely to react appropriately, than the general public.