Post your open position on the Postdoctoral Office "job opportunities" website
2) Make sure to include contact info and a deadline for applications.
The University’s membership with these organizations allows all departments to advertise either for free or at a discounted price. Each department or person registers and sets up their own account, but it is the University email domain that idenifies.
The NPA has an agreement with AAAS and uses their site:
Here are some other well-used sites: