writing
A wonderful quote that is sometimes attributed to Turing Award winner (and LaTeX author) Leslie Lamport is "Writing is nature's way of showing you how fuzzy your thinking is." Writing well is very important in science, both for your own understanding as well as communicating to others, yet it is often difficult for scientists (myself included). Here are some references I have found useful:
In addition (and related) to writing skills, presentation skills are important to communicate scientific results. Simon Jones has some advice, both in a paper (with J. Hughes and J. Launchbury) and in a talk. The talk is a little too powerpointy and cute for my taste, but much of the advice is good.
Finally, check out "The Visual Display of Quantitative Information", by Edward Tufte, for the definitive guide to graphical presentation. Tufte's other books are also worth reading.
problem solving
Here are some useful tips on what to do when you get stuck. Please send me any tricks you find useful, and I'll add them to my list.