Telling the truth. Relying on evidence whenever possible. Parsimony (beautiful word!), i.e., going with the most simple explanation when given a choice. Always, always, turning to others to verify results.
And above all, the rejection of certainty and a corresponding commitment to revising one's thinking when faced with new facts.
Don't let anyone ever tell you that science does not have values.
I found this clip very moving. It's worth watching to the end.