Econsultancy.com's article on the challenges for small and mid-sized businesses, which don't have the brand recognition and bank accounts of large corporations, to recruit great contractors has five great points.
However, I would like to add a sixth, that of appreciation. A contractor, like anyone, likes to feel that his/her work and effort is appreciated and not taking for granted. The difference between an employee and a contractor is that the employee feels more part of the company were as the contractor usually not. If given a choice a contractor will always prefer to work where appreciation is greatest.
1) Negotiating the fee
2) Contracts, NDA, etc.
4) Trust and respect
5) Delivering and follow through
6) Appreciation (my point)