1. Focus on methods and results. Try not to be influenced by the way the study is presented, but rather focus your analysis on the experimental design, techniques, and data.
2. Be a skeptic. Ask yourself how strongly the authors' interpretations and conclusions are supported by the evidence.
3. Be fair. Scientific research is difficult, and scientists operate under many constraints. Don't expect studies to be perfect.
4. Read non-linearly. Exploit the format of research articles to quickly access the information you need. Don't feel compelled to read every line start to finish. Skim the paper to understand its overall approach. Refer to previous sections as necessary.
5. Consider the big picture. Assess where the study fits into the cycle of science, and how it relates to previous research.
6. Consult other sources. Writers of research articles assume their audience has basic knowledge of the area. Consult secondary sources to get the needed background.
7. Take your time. Research articles condense entire studies into a few printed pages. It probably took the authors years to conceive, perform, and publish their work. Be patient and persistent when reading articles.
8. Accept uncertainty. Research articles deal with emerging knowledge and controversial issues. Don't expect to find absolute answers to every question. Each paper is a step in an ongoing process.
9. Expect to be challenged. If you're not an expert in an area, there might be aspects of a paper you can't understand fully. That's OK, you can still learn from those parts of a paper that you can comprehend.
10. Relax and enjoy. Perhaps this is the hardest advice to follow, especially when you're confronted with a complicated paper. But try to approach an article like a puzzle. It's going to take time and effort to make progress, but there's real satisfaction in doing so.
    

From: Gillen, C.M. Reading primary literature: a practical guide to evaluating research articles in biology. Benjamin Cummings, San Francisco. 44p., 2007.