EDC KNIFE and KNIFE SAFETY
Firstly, I always saw my knife as a means of self defense if my life or the life of another was threatened. This sense prompted me to always carry a knife that can be easily opened with a lock that wouldn't fail. Don't be fooled by butterfly knives and switchblades (which are illegal to carry in most states), an easy opening knife will save your life, a fancy novelty knife made too look intimidating won't offer protection and will make you appear less intimidating if your attacker has basic knife knowledge. That's not to say that all switchblades and butterflies aren't well made, I can still appreciate ones that are well made, but I'd rather have something less fancy and more durable to defend myself with.
In daily use, I've used my knives for various small jobs such as cutting boxes open, slicing fruit (after cleaning the blade of course), opening letters, etc...nothing very strenuous. I have a designated "camping knife" for my wilderness trips when I know I'll be shaving bark, cutting rope, or using it to start a fire with my magnesium fire starter.
If you're planning on buying an EDC knife, consider how often you will be using it. Since I don't use mine very often, I didn't need something capable of cutting steel!
So, now you want to choose a knife. The information is out there for you, perhaps start by researching Cold Steel, Buck knives, Gerber, and other quality brands. There's plenty more to be found, I'm just mentioning the brands that I've been pleased with. Consider buying two, one for EDC and one for your survival kit.
Emergency Knife Use:
Above I mentioned my readiness to use my knife for self defense, hopefully I won't ever have to do so. Another emergency use could be freeing yourself from a seat belt in the event of a car crash. If one of your arms is disabled, you may have to use your knife to free yourself by cutting your seat belt. Of course this isn't nice to think about, but it's another reassurance you can have by acquiring a reliable EDC knife.
BASIC KNIFE SAFETY:
ALWAYS CUT AWAY FROM YOURSELF!
This seems like common sense knowledge, so please abide by it.
ALWAYS KEEP YOUR KNIFE CLEAN AND SHARP!
This will lengthen the life and efficiency of your knife. Make sure that the lock is well oiled so you won't have to struggle to put the blade into the open position. If the lock is difficult to use, you increase the risk of hand injury in your attempts to open it.
Keep in mind that an accidental injury with a sharp knife is better than one from a dull knife. A clean cut will be easier to bandage and will heal faster!
DON'T DROP YOUR KNIFE INTO THE DIRT!
If you need to set your knife down, point-first into the ground is never an option. The edge can be easily damaged by unseen rocks.
DON'T THROW YOUR KNIFE!
That's what throwing knives are for!
PASS YOUR KNIFE SAFELY!
Don't pass your knife to a buddy blade first. Hold the back unsharpened edge of the knife (sharpened edge pointing away) and pass it with the handle first. There's no chance for injury passing a knife in this manner, I've had to explain this to several people who have tried handing me a knife by the blade!