As you already know, reading isn’t a “one size fits all” activity: you need to adjust your reading strategies to fit the task at hand. Most instructors probably won’t give you specific instruction in how to read texts; they will simply assume that you know how.
The more you read in any discipline, the easier you will find it to understand—
How does a journal article in this discipline begin?
How is the article organized? Does it have specific sections with subheads?
What sources are cited, and how are they used—
What audience does the text seem to address? Is it a narrow technical or disciplinary audience, or is it aimed at a broader reading public? Is it addressed to readers of a specific journal? Is it published in print, online, or both? Is it intended for an international readership?
How is the text formatted, and what citation style does it use?
How are visuals such as charts or graphs used?
Finally, make sure you know whether articles you are reading are from juried or nonjuried journals. Juried journals use panels of expert readers to analyze proposed articles and recommend publication (or not) to the journal editor, so articles in juried journals have been examined and accepted by experts in the field. Nonjuried journals can also offer valuable information, but they may bear the stamp of the editor and that person’s biases more strongly than a juried journal would.