You can write off all ordinary and necessary expenses incurred to produce your income.
Per the IRS: To be deductible, a business expense must be both ordinary and necessary. An ordinary expense is one that is common and accepted in your trade or business. A necessary expense is one that is helpful and appropriate for your trade or business. An expense does not have to be indispensable to be considered necessary.
See https://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Deducting-Business-Expenses
Some examples:
Business Travel
Communication
Legal and Professional
Meals and Entertainment
Office Expenses
Supplies
Vehicle Expenses