I found this book to be filled with jargon, half baked theories and bizarre assertions. Hubbard seems to only be guessing; he gives no clue as to how he arrives at any of his fantastic claims- that one can raise one's IQ, avoid accidents, pretty much eradicate any and all issues in one's life, by clearing away "engrams" created by bad experiences, including *prenatal* experiences.
In short, one will become more or less superhuman- and if not, it's because you're not doing it right- and it's this weird circular logic that makes the book impossible to take seriously. He seems to have started with some interesting borrowed ideas (regression therapy, ritual magick, etc.) and gotten extraordinarily carried away. In short, he combines older forms of psychotherapy with magical techniques and his own version of Buddhist mindfulness meditation.
This could be of limited usefulness, but I am very concerned that the book makes claims that homosexuality, infertility, etc., are 'perversions,' actual physical illnesses that can be 'cured' by Dianetics, and that ulcers and other diseases are caused by unsuccessful attempts at abortion. These are just two of the many odd medical assertions hubbard makes which could cause serious harm were one to prefer Hubbard's advice over proper medical or pychological care. Most disturbing of all, critics of Hubbard's methods are, of course, ill themselves, criminals, or worse, a frighteningly convenient idea.