If you are in a new area where you haven't worked before, check with the area's film office and ask for crew lists from other productions that have filmed there. Most larger cities have active film offices and each should have crew lists from every film that has shot in the surrounding areas, sometimes the entire state. We recently filmed in Athens, Georgia. Without access to crew lists from other productions through the Georgia Film Office in Atlanta, I would have had a much more difficult time finding our crew.
As you start calling crew and other film professionals, ask for referrals from them as well. Some may not be available or interested in your project, but they may know someone who is. And post jobs on sites like Craigslist and Mandy.com. I've found really good people from ads on Web sites. You can even put the pay to ensure the candidate is already open to the salaries you have budgeted.
Next, schedule sit-down interviews, if you can. You may be out of town and have to rely on phone interviews but if you have the opportunity to schedule an in-person interview, do it. Sitting down with someone will give you the best indication of his or her personality.
Checking references can seem tedious but they can be very revealing about a candidate and they can help you winnow the list of candidates. I'm sure everyone lists references that they know will say good things about them. But, sometimes, references are honest and what they can reveal can help you decide who is best for your production.
You will be spending 12 to 18 hours a day with each crew member and months with others in post. Take the time to hire those you want to spend most of your waking hours with.