I'm so nearsighted I'm probably legally blind without my glasses, but I always take them off. They're distracting. So, bad eyes are no problem.
The main thing is practice. Very dim light, no reflections in the ball. Fifteen or twenty minutes a night until you get results. Do not be discouraged! Some people get results quickly, others take months. Just persevere.
Best books on the subject:
Crystal-Gazing by Theodore Besterman
Crystal Vision Through Crystal Gazing by Frater Achad
Crystal Gazing and Clairvoyance by John Melville
You may notice that all of these were written about 100 years ago! All the contemporary works I have seen on the subject are at best plaigarisations of these, or worse yet, BS like Ted Andrews
Crystal Balls and Crystal Bowls. There is actually a thread here someplace where someone mentions ruining a pricey sphere using his "cleansing" methods. Zolar's
Encyclopedia of Ancient and Forbidden Knowledge gives step-by-step instructions for getting results, and they work - because they were plaigarised almost word-for-word from the Melville book! Zolar also has some VERY racist and ignorant things to say about
what he refers to as "dreamy orientals" and "the tyranny of the Talai (sic) Lama." So, stick with the classics.
Speaking of the Dalai Lama, his
Freedom In Exile mentions Regent Rinpoche successfully scrying in the sacred vision lake Lhamo Lhatso in order to locate his new incarnation, and also the Tibetan art of
Ta, gazing in a polished silver mirror. Much nicer than the Zolar book.
You might also be interested in F.W.H. Myers
Human Personality and It's Survival of Bodily Death, for crystal gazing anecdotes as well as some other very interesting accounts.
Enjoy! And let us know if you have any more questions.