1. Always have a written contract. You wouldn't hire an electrician without so why are you working with an independent contractor without one?
2. Treating similar workers differently. Having two employees who perform the same job with one paid hourly and some as independent contractors could be problem.
3. Providing tools and supplies. Under the Independent Contractor test, you must prove that they supply their own tools.
4. Reimbursing expenses. This may become a problem if you reimburse employees.
5. Paying by the hour. Do not pay independent contractors by the hour.
6. Over supervising. Usually your paying for a product or a specific result.
7. Requiring set hours. See 6.