If you are working in the US - but you are not an US citizen - you are treated as a resident alien for income tax purposes.
That means - you should report all your worldwide income on your US tax return.
So if you run a business as a solo proprietor - there would not be any difference for income tax purposes, but the owner will be taxed on net business profit - and will be subject to both - income and self-employment tax.
You will report your income and may deduct qualified expenses.- you may report all business income and expenses -
on the schedule C -
The net income (after deductions) will be reported on the form 1040 line 12 -
If the business has net income over $400, it may be required to file Schedule SE, Self-Employment Tax
and net self-employment income is subject to 15.3% self-employment tax.
Self-employment taxes from schedule SE will go to the form 1040 line 57 -
Also - you will deduct half of self-employment taxes on the line 27.
Generally - that all you needs tax purposes.Please review all possible deductions - that might help to reduce income tax liability.
Now - if the same income is taxed in the US and in Mexico - you will claim a foreign tax credit on your US tax return where you are a resident - and effectively will avoid double taxation of the same income.