Science writer Gary Taubes on Richard Feynman and good science:

...In a commencement address that Richard Feynman gave at Caltech in the 1960s, he said that "the first principle [of science] is that you must not fool yourself -- and you are the easiest person to fool."

So the simplest way to think about it is that good scientists are the ones who are most aware of this fact: how easy it is to be fooled by their data and to fool themselves. They're the ones who are most skeptical about their own work, not just the work of others. They're also aware that the only way not to be fooled is to work relentlessly to try to disprove your own pet theories, not try to confirm them.

Bad scientists do one experiment, get some interesting result, decide they've discovered something new, and then spend the rest of their lives trying to somehow prove that they did. Again, science doesn't work that way.

You have to put more faith in negative evidence than in positive; you have to put more effort into trying to refute your own beliefs and hypotheses, rather than trying to prove them. If you fail to refute them, then you can begin to take them seriously. And, yes, the inventors of cold fusion were bad scientists.

The rest of the interview has some interesting discussion of food and nutrition as well.