I had a contractor come on board who has always been a W2 employee before. Here is the advice from my CPA for contractors.
Independent contractors need to make estimated payments. As an independent contractor, you are responsible for paying all the taxes on your earnings. To do this, you make quarterly estimated tax payments to the IRS using Form 1040-ES. In addition to federal and state taxes, independent contractors need to pay a self-employment tax of 15.3 percent of earnings.
Tip: Track your expenses and save receipts. By doing this, you can subtract eligible expenses like mileage, supplies and uniforms from your gross earnings. Use this lower income number to calculate your self-employment tax and correctly estimate your income tax obligation.