Rule 9. Another tough rule: You must not divert money into the system which you would have got anyway had you not been doing the system. You must always use the stake money to gain the next step. Essentially then, you must trade to achieve each step, rather than work (in employment) to achieve it. You may take on extra work outside of your normal field of occupation, but I warn you now that there are strict limits to how far you will get using this approach. Trade, don't work.
Rule 9. Detail. The money gained must be NEW money. Money you wouldn't normally have got unless you had started the doubling system. For example, you are on step 10 and struggling for a way to get to step 11. It is not permissible to work a few extra hours down the pub (or wherever you normally work) to get the money. You could have done this anyway, it is not 'new' money. Also, you are not employing the stake money to achieve this step.
Supposing you are already running a small business. You are not allowed to use stake money to buy and sell within your existing field of operation (using overheads paid for outside of the system). This is not new money and you are using all sorts of 'hidden' advantages (existing products, customer loyalty, etc.) to help you achieve this step. You could have done this without the system.
As a rule of thumb, you should trade in totally unrelated areas to your normal employment or business.