While knowledge and equipment can save your life, awareness keeps you from having to fight for it. Be aware of what to expect, such as weather, climate, flora, fauna and special hazards: rocks falling, landslides, quicksand, and flash floods. Listen when you are outside. Know the sounds of thunder, rushing water, large animals in brush and fire, for example. Look around you; don't be so absorbed in where your feet are that you forget to look ahead, and sometimes, even behind you. No matter what dangers you might imagine, more people are killed by lightning (even on cloudless, clear days) than any other type of accident. Know your lightning safety facts so you can avoid needing to use them (see Resources section below).
Knowledge of the Outdoors
You need knowledge to be outside, and you should tailor that knowledge to your outdoor activities. Anyone doing a sport in, on or near water needs to know basic swimming and life-saving, as well as facts about hypothermia and energy conservation if faced with open water. Do your homework about boat safety, rising water, walking in shallow fast water and all applicable scenarios for your situation. It isn't enough to wear a PDF (personal flotation device) if you've hit your head on a boat or been swept out to sea. Having a helmet when rock-climbing is good, but it won't help if you break a leg and don't know what to do. If hiking, know the basics. In "How to Stay Alive in the Woods," Bradford Angier suggests to "never step on anything you can step over, and never step over anything you can walk around." Know what safety risks you'll face and how to avoid them.
Appropriate footwear and clothing is essential, even for day hikes, and if you plan to go into back country, you need to know basic emergency skills (see Resources section). Having the right gear for your sport or past-time is good, but having the right clothes and protection for your body is vital. A hat, sunscreen, shades and long, light clothes are needed in hot, sunny areas, but I am always shocked at how many people go on desert hikes in shorts and flip-flops with none of the above. Insulation is crucial for cold and wet climates, and always pack a jacket or thermal protection when at high elevations or water bodies where weather can change in an instant. A little bug spray goes a long way, and unless you like being swarmed or covered in ticks,smelling like citronella or chemicals might be better. Know the limits of your gear like tents and sleeping bags, and test them before using---to be certain you'll stay dry and warm.
Know how to find water and food if you are separated from your own supply. Water runs downhill, but you can avoid some fairly awful diseases by filtering and boiling water before drinking. And drink you must. Your body can live without food for weeks, but only days without water, and not even that long in some climates. "Hydrate or die" is one motto to remember, but frequently people hike with no water, or one teeny bottle for a whole family. Carry easy-to-eat, high-calorie snacks like trail mix or granola for emergencies---and it doesn't hurt to have a little knowledge about what in the wild is okay to eat and what isn't. Never eat anything (like a mushroom or plant) unless you are absolutely sure it is safe.
"Fail to plan, plan to fail," is a favorite quote for outdoor adventurers everywhere (although no one can agree who said it first). But your plan should have a back-up. Have a good first-aid kit, and a basic emergency kit right for your activity (fire-starting flint, emergency blanket or garbage bag, knife or multi-tool, compass and signaling mirror or lens). Knowing what to do in an emergency is much better than all the gear in the world. A compass is no good if you misread it, but the position of the sun and stars are useful if you know how to use them. Fire-starting is a good skill for anyone who goes beyond the reach of civilization, even for an afternoon, and knowing how to administer first aid in the field is as crucial as carrying a kit.