Here is something I read in graduate school and still thinks about from time to time:

Edsger W. Dijkstra's Three Golden Rules for Successful Scientific Research:

  1. Raise your quality standards as high as you can live with, avoid wasting your time on routine problems, and always works as closely as possible at the boundary of your abilities. Do this, because it is the only way of discovering how that boundary should be move forward.
  2. We all like our work to be socially relevant and scientifically sound. If we can find a topic satisfying both desires, we are lucky; if the two targets are in conflict with each other, let the requirement of scientific soundness prevail.
  3. Never tackle a problem of which you can be pretty sure that (now or in the near future) it will be tackled by others who are, in relation to that problem, at least as competent and well-equipped as you.

(Ref: http://userweb.cs.utexas.edu/~EWD/transcriptions/EWD06xx/EWD637.html)