I do a lot of independant contracting. The best way it was described to me was this test, does the independant contractor make it's own managerial, marketing, purchasing, and labor cost decisions? If so they'r an independant contracator, if not, they're an employee. Two examples.
Company hires a website dev who purchased own computer, markets himself/herself, and sets their rates would be an independant contractor.
Now if a company provides a computer/software or sets the hourly rate in which that person will receive it's an employee.
Contractor hires an indepentant contractor for landscape. That landscaper doesn't set schedule or completion date, doesn't set price is now an employee, not an indepentant contractor. In order to be considered an indepedant contractor he/she must set their own price and completion date.
In short all manager level decisions, all tools or supplies used, price, and project timelines/dates must be set by independant contractor.