Employees are entitled to benefits by statute, but independent contractors are not. An independent contractor relationship can be established by contract, as for example with a consultant, mechanic, serviceman, professional, etc. See Avvo's consulting agreement template to get a sense of what you'll need to include.
Keep in mind though, it takes more than just a well-written agreement for a court to define a person as an independent contractor. According to the modern legal test, the worker must actually be treated like an independent contractor rather than an employee. The key is independence. The more independence given to the worker, the more likely a court will deem that person an independent contractor.
Each of the following factors are used by courts to test whether a person is truly an independent contractor, but no single factor by itself can decide the issue: