When it comes to your career, the only thing more valuable than your experience is your reputation. Unfortunately, the latter is much easier to tank than the former. After all, no matter how many times you lose your temper, you get to keep your CV.
Having strong references can mean the difference between hearing, "You're hired!" and hearing nothing but dreaded silence. I've often covered the most appropriate methods of acquiring references, including asking permission, providing them with information about the position, and keeping them up-to-date with the overall process. This methodology is great if you already know who your references are, but where do you begin when you're not even sure who to ask?