It's not a great start for 50 Cent's book on business when a fake tattoo slips from its pages. That's hardly "keeping it real" in a tome that tries hard to look biblical with its black cover and gold lettering, gilt-edged pages and the odd bit of purple.

Things don't get much better after that. The central premise is that "your fears are a kind of prison that confines you within a limited range of action. The less you fear, the more power you will have and the more fully you will live". This is what the authors call 'the 50th Law', an ability to overcome anxiety and live life fearlessly. Apparently its followers are quite the homogeneous group, possessing "supreme boldness, unconventionality, fluidity and a sense of urgency". Sounds remarkably like opening night on Big Brother to me.

Just in case you're a sceptic, Greene marks your cards early. There are warnings that if you think "the streets that moulded 50 and the code he created for himself" have little to do with you, then "that is merely a symptom of your dreaming, of how deeply you are infected with fantasies and how afraid you are to face reality". In fact "you need this code even more than 50". But, perhaps in recognition of the target market, when the authors tell you that you have to become a better observer of people in order to advance yourself, it is pointed out that "this cannot be done on the internet". Strange then, that they make such a big deal of how 50 interacts with his fans through his website, of all things.

There is constant repetition of anecdotes with a small detail added each time around and, in an already tedious book, this becomes irritating by the halfway mark. There's also almost no mention of 50 Cent's deal with Glaceau's VitaminWater, which earned him a nine-figure sum. The rapper took a stake in the company in return for endorsing it and, when Coca-Cola bought Glaceau for more than $4bn, it seemed Fiddy was set to earn $400m. Forbes magazine says the true figure was $100m but still, it's hardly chump change and it's surprising that it attracts so little attention or detail. However, the book then says that, when it came to endorsement deals "that would make him some fast millions", 50 Cent "would turn them down, opting to star his own businesses on his own terms". Hmmm.

Greene lauds the rap star's acumen in getting signed by Eminem's Interscope three years after being dropped by Columbia, a decision made after 50 was shot nine times by an "assassin". But one senior executive had told him he could possibly be re-signed after two years. Strange that. Equally strange is the song he released afterwards, apparently "summarising how he felt about his killers". Perhaps he's an angel too?

Much emphasis is also placed on how 50 Cent diversified and avoided direct major label control but in truth the blueprint had been set out years beforehand, with credibility in some cases (Jay-Z) and commercial success (P Diddy) in others.

There's something intensely spirit-crushing about this book, which basically advises people to charge straight in and, if that doesn't bring success, to plot and scheme in the background. It's all about the cult of the individual. That might lead to wealth but then Greene finds it necessary to thank his cat Brutus in the acknowledgments. No prizes for irony there. As it is, the book will probably appeal to the suburban white boys who form 50's main audience... before they head off to the Chicago School of Economics to learn how to destroy another country.

The 50th Law By 50 Cent and Robert Greene, Profile Books, £15.99

Neil Callanan is deputy business editor of the Sunday Tribune