Recently, a student wrote to me asking for advice on the process of choosing his graduate adviser at the university he's going to start attending this fall. There are posts in this blog under the label HigherEd - Advice meant for people like him.
In particular, this post has links to advice from Sean Carroll and Chad Orzel; both of them emphasize the importance of choosing one's adviser. If you make a misstep, life could become miserable (here are two examples:from India and from the US).
In you are like what I was when I entered grad school, you are broadly aware of what interests you, and more acutely aware of what you loathe. Clearly, this is the first filter: you certainly don't want to spend N years (where N is typically 5 years or longer) working in a subfield that repels you. This filter gives you a preliminary list of potential advisers.
Now you use the second filter: get rid of 'jerks' (aka 'assholes') from your list! The argument is similar to that used for the first filter: you don't want to spend the next N years working with someone who's known to be toxic; worse, he/she will have a lot of power over you!
For the first filter, your prior experience is the guide. What about the second filter? How do you figure out who's a jerk? Use every possible resource at your command: scour the web, search blogs, and lurk around social networking sites where you might pick up some gossip. If you know someone (who knows someone who knows someone ...) at the university you plan to attend, tap them for inside information and knowledge.
After you get to your university, you would normally get some time before you choose your adviser. Use this opportunity to talk to not only the potential advisers, but also their students. Visit them in their labs, and check out the atmosphere there. Keep your eyes and ears open for anything sinister.
Bottomline: Do everything you can to figure out who the jerks are. And avoid them.
Corollary: If it takes some time before you discover the jerk in your boss, it's never too late. Dump him/her immediately, and move on: change your adviser, university, field, line of work, whatever! Life is too short and precious to spend around nasty people.
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Jerk avoidance is important not only for graduate students and post-docs (whose advisers have enormous power over them, sometimes for a big chunk of the rest of their professional careers), but also in business settings. Do read Building the Civilized Workplace (free registration required) by Stanford's Bob Sutton who recently published he No Asshole Rule: Building a Civilized Workplace and Surviving One That Isn’t. Sutton blogs here.