A good place to start is Schedule C; a large number of the most common deductions are listed there. Do not forget miles (you did keep a milage log? Right?). A written record of miles and the purpose of the trip is required for a deduction. The same applies to meals and entertainment. Other deductions just require a receipt.
A mobile hairdresser probably has some advertising expense, supplies (product), office expense, and bank fees. Anything related to the business is deductible or depreciable. Purchased assets with a life in excess of one year must be depreciated or expensed. Section 179 expensing is limited, check Form 4562.