Always always always use a holster with a Glock when carrying.

I always reholster only after taking it off, inserting gun, then putting it back on.

Don't play quick-draw to impress your friends. Don't ever stuff it in your pants Mexican carry style and you will be fine.

Did I mention always use a holster? Use it as designed, your finger is the #1 best safety device, never put it on the trigger unless you are ready to shoot.