It takes time to mount an effective job search, but it only takes a moment to kill one.
1. Bemoaning a long, demanding job search
Even if you have been on the market for a long time, find any way to make your efforts seem positive, as though you took the time off by choice. Make it appear as if you have enjoyed your time networking with various contacts.
2. Getting impatient with the process
Understand that the hiring decisions can drag on for weeks, if not months. Pestering your contacts frequently, by either phone or email, will not speed up the process and only hurt your chances.