Defensive Back Pass Coverage?

I'm going to play Safety in football next year... anyone have tips on pass coverage? Also, whenever I man-to-man cover someone, how am I supposed to know when to look for the ball? Lastly, are there such things as prescription visors? I have pretty poor eyesight, and sports prescription goggles look kinda funny, so I wanna know if there's anything I can do instead of wearing the goggles.