Here's another of my guerrilla videos (make sure you turn the volume way up to hear the voice over). This one is about how to make a proper fist. I have contact with hundreds of aspiring martial artists every year. Virtually none of them--and I would quantify 'virtually none" as 1 out of a 100 -- know how to properly form a fist with their hands. All of them roll their hands up thinking that they are making a fist, but in actuality, they would damage their hands if they ever hit something solid with it.
Over time I will talk extensively about hitting with your hands, but for now, take a look at this video and, please, do as it says before you go and hit anything,,,a pad, a punching bag, another person (in self defense or in sparring) with it.