"write clearly -- don't sacrifice clarity for 'efficiency'"<p>"make it clear before you make it faster"<p>"make it right before you make it faster"<p>"keep it simple to make it faster"<p>From "The Elements of Programming Style" by Kernighan and Plauger<p>Other than that maybe that naming is one of the hardest and most important things to do.
Learn when the most productive thing you can do is look out the window for 15 minutes.<p>Quit when you're tired.<p>When there's something that took you a while to figure out (like what the command line arguments are to get the compiler to produce a link map, say), write it down in a file of such info.