Most of the time, skimming through, picking out the parts that are different from others in the field. For physics: "Okay, this paper is from so and so, yup, s

Most of the time, skimming through, picking out the parts that are different from others in the field. For physics: "Okay, this paper is from so and so, yup, same facility and equipment as the previous one. Theory section, same basic overview, skip to the end for what makes this experiment worthwhile? Anything interesting in their analysis, and how good are their statistics? Did they show the usual set of diagnostics plots for the type of analysis they did, and if not, what are they trying to downplay?"