To be clear, it is not possible to avoid risk. The goal is to minimize the risk, and to control the outcome of exposure to risk.
For starters it is ideal to understand the laws governing your state as well as the country or state your contractor resides in (and/or conducts business in).
I recommend you record everything from ims, to phone calls to, emails. It is not sensible to assail people over the finer points of what has been said but it is valuable to keep people honest, and to make sure both parties are clear on the expectations.
Assume nothing. No one works quite the way you do so anything you don't specifically state is open to interpretation. Be wary however, in the US you can specify the details of a job for contract workers but you cannot specify how they perform the work (eg during the day, etc). Once you do they become an employee and your relationship as well as your obligations, change dramatically.
Always use a contract. It may not even hold up in the contractors state or country but it serves well to clarify expectations which helps both parties.
Lastly, most people don't consider this but, be fair and honest with the people you work with. This is no guarantee by far that you will be dealt with in kind, but treating people like they are enemies or criminals certainly is.