Write offs include supplies for your business, repairs to your equipment, auto expenses for travel to sites (travel to office is considered commuting and not deductible), telephone expenses directly related to your business, advertising, insurance, home office IF you meet the very strict criteria, that allows you to write off part of your electric, rent/mortgage, etc but it is a red flag so be very sure you follow the rules exactly. You can write off depreciation of major equipment buys (car, computer, etc) provided they are strictly business. Look online at a schedule C. It details what can be deducted.
You can write off on your taxes as per the assets that you might have purchased for use in a trade or profession that has a valuable life further than one year to be entitled for decline deductions. It is essential for you to first verify internal revenue publications. You may confer with a tax advisor for an entire list of deductions and how to submit an application.