Under part 2, question #2, if you working (illegally, of course), you should provide your income accurately. This number should be reported even if you were being paid under the table. It is tempting to not report your income on which you are not paying taxes or your employer is doing something fishy, but if you do not tell the truth, you will be lying, and that is worse. If you lie is caught, your application will definitely be rejected. The worst outcome in the other case is that you might owe some back taxes, though, most experts doubt if things will work like that.
Under part 2, question #3, put a total of all your expenses. If you live with your family, you can divide the cost of food, housing, etc. among all the members, and report a number for you. Obviously, expenses that are only for you, like education, car, phone, books, etc. should be included.
Under part 2, question #4, include the money you might have in the bank or any other valuables that you might own. Your clothes and cell phone do not count, but include the value of a car, land, stocks, homes, jewelry, etc. even if they are overseas. Merely owning assets will not disqualify you from a work permit. The USCIS understands that you want to work even if you do not need the money to survive, because someone did not go to nursing school to sit at home her whole life.
In part 3, you can provide an explanation if something is out of the ordinary. For example, if you have huge assets outside the United States, you can explain why you do not have access to the assets to pay for your expenses. However, if you have low income, reasonable expenses, and little or no assets, then, there is no need for any explanation.