Two essays on being successful in graduate school that my students have found useful:

1. "Some modest advice for graduate students" by Stephens C. Stearns can be viewed at: http://www.eeb.yale.edu/stearns/advice.htm

or downloaded as a pdf file from here

2. "On being a successful graduate student in the sciences" by John N. Thompson can be downloaded at: http://bio.research.ucsc.edu/people/thompson/Prospective.html

or downloaded as a pdf from here