Best advice for new PhD students

This one is easy. Although you think you're doing a PhD to engage in research--and you are--you also need to be learning about the vagaries of the academic job market. Aside from books about an academic career, some of which I've reviewed for the blog, the other good source of information is the Chronicle of Higher Education forums, which are free. (The subscription-based CHE weekly journal is also very useful and you'll probably have some form of proxy access through your university library.)

Here are two threads from the forums to get you started:
What have we learned this year?
Worst advice about the academic job market

Cautions about the CHE forums:

• Remember that this is online and searchable, so if you participate, be careful not to reveal so many details that you'll lose anonymity, unless you're treating your online persona as one that could be recognized as you from the very beginning.
  
• Take the advice with a grain of salt -- There is a huge variety of opinions and experience in the forums, as with most things online. Moreover, your field may have different conventions than people in other fields, so try to give some pointer to the area, even if you don't want to disclose your particular field (eg. social science, humanities).
• Be nice. Oh, you can be mean if you want to, but the results aren't pretty, and there are few people who can be as snarky as an English professor who's in the 7th year of the tenure track job search.
  
• Don't be a snowflake. This is the common term for inexperienced students, whether demanding undergrads or clueless people in grad programs. People may be unkind to you if you ask stupid questions before doing a search of the previous posts. For example, I saw someone post the question "Can I list my blog on my CV under publications?" Sigh. The results were about what you'd expect.
• Please don't use "hu" for he/she/they. (That's my pet peeve.)
  
• Don't spend all your time on the CHE forums, which could make you too depressed and cynical. Spend more time in the lab, writing up results, and most importantly, getting papers ready for journal submission.